Red Seal Refrigeration and Air Conditioning Mechanic (313A) — Questions and Answers

Question 1: What maintenance should be performed on evaporator coils?

Only the condenser requires regular maintenance
Regular cleaning of fins and drain pan, checking drain lines, verifying airflow, and inspecting for corrosion or refrigerant leaks (Correct answer)
Evaporator coils are maintenance-free
Only replace the entire coil when it stops working

Correct answer: Regular cleaning of fins and drain pan, checking drain lines, verifying airflow, and inspecting for corrosion or refrigerant leaks

Evaporator coil maintenance includes: cleaning fins with appropriate coil cleaner (to remove dust, mould, and biofilm), cleaning and sanitizing the condensate drain pan, flushing drain lines to prevent blockages, checking airflow across the coil, inspecting for corrosion or refrigerant leaks, and replacing air filters regularly to reduce coil fouling.

Question 2: What colour coding identifies a recovery cylinder versus a refrigerant-specific cylinder?

Recovery cylinders are red with white tops
Recovery cylinders are grey with yellow tops; specific refrigerants have designated colours (e.g., R-410A is rose/pink, R-22 is green) (Correct answer)
All cylinders are the same colour
Recovery cylinders are always white

Correct answer: Recovery cylinders are grey with yellow tops; specific refrigerants have designated colours (e.g., R-410A is rose/pink, R-22 is green)

Recovery cylinders used in Canada are identified by a grey body with a yellow shoulder/top. Specific refrigerant types use designated colours: R-22 (green), R-134a (light blue), R-410A (rose/pink), R-404A (orange). Since 2004, the ARI assigned grey with the same coloured band to prevent misidentification, but older colour coding persists.

Question 3: What is an electronic expansion valve (EEV) and what advantages does it offer?

An electrically heated capillary tube
A stepper-motor or pulse-width-modulated valve controlled by a microprocessor that adjusts refrigerant flow based on multiple sensor inputs for precise superheat control (Correct answer)
A solenoid valve that is either fully open or fully closed
A motorized ball valve for refrigerant isolation

Correct answer: A stepper-motor or pulse-width-modulated valve controlled by a microprocessor that adjusts refrigerant flow based on multiple sensor inputs for precise superheat control

An EEV uses a stepper motor or pulse-width modulation controlled by a microprocessor to precisely regulate refrigerant flow. It reads multiple inputs (suction temperature, evaporator pressure, discharge temperature) to optimize superheat and system performance across all operating conditions, offering superior efficiency and control compared to TXVs.

Question 4: What is the purpose of the oil separator in a refrigeration system?

To separate non-condensables from the refrigerant
To remove moisture from the refrigerant
To filter particulates from the liquid line
To separate compressor oil from the discharge gas and return it to the compressor crankcase (Correct answer)

Correct answer: To separate compressor oil from the discharge gas and return it to the compressor crankcase

An oil separator is installed in the compressor discharge line to capture oil entrained in the hot gas and return it to the compressor crankcase, preventing oil loss and maintaining lubrication.

Question 5: Under Canadian OHS regulations, what is required before a technician enters a confined space that may contain refrigerant vapour?

Wearing a dust mask and carrying a flashlight
A brief visual inspection of the space from the entrance
Notification to the building owner at least 24 hours in advance
A confined space entry permit, atmospheric testing for oxygen level, flammable gases, and toxic contaminants, and a standby person outside the space (Correct answer)

Correct answer: A confined space entry permit, atmospheric testing for oxygen level, flammable gases, and toxic contaminants, and a standby person outside the space

Provincial OHS regulations across Canada require a formal confined space entry program including written permits, atmospheric testing (O2, flammable gas, toxic substances including refrigerants), and a trained attendant outside before any worker enters a confined space.

Question 6: What is the purpose of the reversing valve in a heat pump system?

To redirect refrigerant flow so the indoor coil acts as a condenser (heating) or evaporator (cooling), switching the system between heating and cooling modes (Correct answer)
To reverse the direction of airflow through the air handler between seasons
To reverse the direction of compressor rotation for heating and cooling modes
To switch the electrical polarity of the compressor motor for reverse operation

Correct answer: To redirect refrigerant flow so the indoor coil acts as a condenser (heating) or evaporator (cooling), switching the system between heating and cooling modes

The four-way reversing valve redirects refrigerant flow in the system so that the indoor coil can function as either a condenser (releasing heat for heating) or an evaporator (absorbing heat for cooling), giving the heat pump dual-mode capability.

Question 7: What effect does a low evaporating temperature have on compressor capacity?

It has no effect on compressor capacity; only discharge pressure affects capacity
It decreases compressor capacity because suction vapour density decreases, reducing the mass of refrigerant pumped per revolution (Correct answer)
It increases compressor capacity because more refrigerant vapour is produced
It increases capacity in scroll compressors but decreases it in reciprocating compressors

Correct answer: It decreases compressor capacity because suction vapour density decreases, reducing the mass of refrigerant pumped per revolution

At lower evaporating temperatures, suction pressure decreases and the refrigerant vapour becomes less dense; since the compressor displaces a fixed volume, less refrigerant mass is moved per revolution, reducing capacity.

Question 8: What is R-744 and what is its main advantage as a refrigerant?

It is CO2; its GWP is 1 (the baseline), making it extremely climate-friendly (Correct answer)
It is R-134a with a UV dye tracer; its advantage is leak detection
It is propane; it is cheap and widely available
It is R-410A blended with nitrogen; it is non-flammable

Correct answer: It is CO2; its GWP is 1 (the baseline), making it extremely climate-friendly

R-744 is carbon dioxide (CO2), and because GWP is referenced to CO2, its GWP is exactly 1, making it one of the most climate-friendly refrigerant options available.

Question 9: What does a current transformer (CT) do in an HVAC monitoring or protection system?

It converts three-phase current to single-phase for metering purposes
It converts AC current to DC current for electronic control boards
It steps up voltage from 24V to 120V for control circuit power
It produces a small secondary current proportional to the high primary current flowing through a conductor, allowing safe measurement and monitoring of large currents (Correct answer)

Correct answer: It produces a small secondary current proportional to the high primary current flowing through a conductor, allowing safe measurement and monitoring of large currents

A current transformer clamps around a conductor and inductively produces a proportional, much smaller secondary current (typically 0-5A AC) that is safe to connect to metering or protection relays without direct connection to the high-current circuit.

Question 10: A system has low suction pressure, low discharge pressure, normal subcooling, and high superheat. What is the most likely diagnosis?

Refrigerant overcharge
Dirty condenser coil
Refrigerant undercharge (Correct answer)
Faulty compressor discharge valves

Correct answer: Refrigerant undercharge

Low suction pressure combined with high superheat and low discharge pressure indicates insufficient refrigerant in the system — the evaporator is starved of liquid, causing high superheat, and the compressor is moving less vapour mass, lowering both pressures.

Question 11: What does a bubbling sight glass indicate when the system is at steady-state operation?

The TXV is functioning correctly and modulating flow
The condenser fan is operating at reduced speed
Refrigerant shortage, moisture contamination, or a restriction causing partial vaporization of the liquid upstream of the sight glass (Correct answer)
Normal operation with a full liquid line

Correct answer: Refrigerant shortage, moisture contamination, or a restriction causing partial vaporization of the liquid upstream of the sight glass

A bubbling or foamy sight glass at steady state indicates the liquid line contains vapour bubbles, which can be caused by low refrigerant charge, excessive pressure drop, or a restriction in the liquid line producing flash gas.

Question 12: What does the term 'zeotropic blend' mean for refrigerants such as R-407C?

A refrigerant that cannot be separated into its components
A blend of refrigerants with different boiling points that exhibit a temperature glide during phase change (Correct answer)
A refrigerant blend that behaves as a single pure fluid with no temperature glide
A natural refrigerant with zero GWP

Correct answer: A blend of refrigerants with different boiling points that exhibit a temperature glide during phase change

Zeotropic blends are mixtures of refrigerants with different boiling points; they exhibit temperature glide — the temperature changes during evaporation and condensation at constant pressure — which must be accounted for in system design.

Question 13: What is the difference between a fin-and-tube evaporator and a plate evaporator?

There is no significant difference
A fin-and-tube is for heating only; a plate is for cooling only
They use different refrigerants
A fin-and-tube uses tubes with attached fins for air-cooled applications; a plate evaporator uses stacked plates for liquid-cooled or direct-contact applications (Correct answer)

Correct answer: A fin-and-tube uses tubes with attached fins for air-cooled applications; a plate evaporator uses stacked plates for liquid-cooled or direct-contact applications

Fin-and-tube evaporators use copper or aluminium tubes with aluminium fins pressed onto them to increase surface area for air-to-refrigerant heat exchange. Plate evaporators use corrugated stainless steel plates to create channels for refrigerant and the fluid being cooled, offering high efficiency in compact liquid-cooling applications.

Question 14: What does 'latent heat' refer to in refrigeration?

Heat generated by electrical resistance
Heat absorbed or released during a phase change without a temperature change (Correct answer)
Heat lost through conduction in metal pipes
Heat that causes a temperature change

Correct answer: Heat absorbed or released during a phase change without a temperature change

Latent heat is the energy absorbed or released when a substance changes phase (e.g., liquid to vapour) at a constant temperature, which is the principle behind refrigerant phase changes in the cycle.

Question 15: What is a hard lockout versus a soft lockout on an HVAC safety control?

Hard lockout uses a physical lock; soft lockout uses a digital code
Hard lockout is for commercial; soft lockout is for residential
A hard lockout requires manual reset after a safety trip; a soft lockout automatically resets after the fault condition clears or after a timed delay (Correct answer)
They refer to the same type of reset

Correct answer: A hard lockout requires manual reset after a safety trip; a soft lockout automatically resets after the fault condition clears or after a timed delay

A hard lockout safety control requires a technician to manually reset it (by pressing a button or cycling power) after it trips — ensuring a qualified person investigates the cause. A soft lockout automatically resets when the fault condition clears or after a timed delay. High-pressure switches are often hard lockout; low-pressure switches may be soft lockout.

Question 16: What are the three main types of compressors classified by their housing?

Open (external drive), semi-hermetic (serviceable), and hermetic (welded/sealed) (Correct answer)
Rotary, centrifugal, and axial
Low-pressure, medium-pressure, and high-pressure
Single-stage, two-stage, and multi-stage

Correct answer: Open (external drive), semi-hermetic (serviceable), and hermetic (welded/sealed)

Compressors are classified by housing type as: open (motor is external and connected by a shaft coupling, allowing motor service), semi-hermetic (motor and compressor in a bolted housing that can be opened for service), and hermetic (motor and compressor welded in a sealed shell, not field-serviceable).

Question 17: What is the purpose of an oil separator in a refrigeration system?

To mix oil with the refrigerant for better lubrication
To remove water from the oil
To cool the compressor oil before recirculation
To separate compressor oil from the hot discharge gas and return it to the compressor crankcase, preventing oil logging in the system (Correct answer)

Correct answer: To separate compressor oil from the hot discharge gas and return it to the compressor crankcase, preventing oil logging in the system

An oil separator is installed in the discharge line to separate compressor lubricating oil from the high-pressure refrigerant gas. It returns the oil directly to the compressor crankcase, preventing oil from travelling through the system and accumulating in the evaporator or condenser where it reduces heat transfer efficiency.

Question 18: What maintenance should be performed on a semi-hermetic compressor that cannot be done on a hermetic compressor?

Internal service including valve plate inspection/replacement, bearing inspection, motor winding checks, and oil analysis (Correct answer)
Electrical terminal tightening only
Refrigerant recovery only
External cleaning only

Correct answer: Internal service including valve plate inspection/replacement, bearing inspection, motor winding checks, and oil analysis

Semi-hermetic compressors have a bolted housing that can be opened for internal service, unlike welded hermetic units. Technicians can inspect and replace valve plates, check bearing condition, inspect motor windings for damage, analyze and change oil, and replace gaskets — extending the compressor's serviceable life.

Question 19: What type of condenser uses water as the heat rejection medium and is commonly used in large commercial systems?

Water-cooled condenser (shell-and-tube or plate heat exchanger) (Correct answer)
Desuperheating condenser
Evaporative condenser
Air-cooled condenser

Correct answer: Water-cooled condenser (shell-and-tube or plate heat exchanger)

Water-cooled condensers, such as shell-and-tube or brazed plate heat exchangers, use water from a cooling tower or municipal supply to reject heat from the refrigerant, offering high efficiency in large commercial applications.

Question 20: What is the purpose of a high-pressure safety switch (cutout) on a refrigeration system?

To increase the pressure for faster cooling
To regulate the normal operating pressure
To shut off the compressor if discharge pressure exceeds a safe limit, preventing equipment damage or rupture (Correct answer)
To control condenser fan speed

Correct answer: To shut off the compressor if discharge pressure exceeds a safe limit, preventing equipment damage or rupture

The high-pressure cutout is a safety device that opens the compressor control circuit if the discharge (head) pressure exceeds a predetermined setpoint. This protects against conditions such as condenser blockage, overcharge, non-condensable gases, or condenser fan failure that could cause dangerous pressures or compressor damage.

Question 21: What is a flooded evaporator and where is it typically used?

An evaporator damaged by water flooding
An evaporator with excessive frost buildup
An evaporator with too much refrigerant — a fault condition
An evaporator where the tubes are submerged in liquid refrigerant, used in large chillers to cool water flowing through the tubes (Correct answer)

Correct answer: An evaporator where the tubes are submerged in liquid refrigerant, used in large chillers to cool water flowing through the tubes

A flooded evaporator is a shell-and-tube design where refrigerant floods the shell side, submerging the tubes that carry the fluid being cooled (typically water). Liquid refrigerant is maintained at a level covering the tubes, ensuring efficient heat transfer. This design is common in large centrifugal and screw chillers.

Question 22: What are the three types of condensers used in HVAC systems?

Horizontal, vertical, and diagonal
Primary, secondary, and tertiary
Air-cooled, water-cooled, and evaporative condensers (Correct answer)
Plate, shell, and tube

Correct answer: Air-cooled, water-cooled, and evaporative condensers

The three types of condensers are: air-cooled (uses ambient air and fans), water-cooled (uses water circulated through a cooling tower or city water), and evaporative (combines air and water spray for enhanced cooling). Air-cooled is most common in residential and light commercial; water-cooled offers higher efficiency in larger systems.

Question 23: A system has been operating normally for a long time but now shows gradually rising discharge pressure and head pressure over several weeks. The condenser coil is clean. What is a likely cause?

Non-condensable gases (air or nitrogen) accumulating in the system from a low-side leak or improper service procedure (Correct answer)
Low ambient temperature reducing condenser performance
Refrigerant undercharge developing from a slow leak
Compressor suction valves beginning to fail

Correct answer: Non-condensable gases (air or nitrogen) accumulating in the system from a low-side leak or improper service procedure

Non-condensable gases accumulate at the top of the condenser and raise head pressure over time; if the source is a low-side leak (suction pressure below atmospheric), air can be drawn in, gradually building up non-condensables in the system.

Question 24: What is the purpose of calculating the refrigeration effect in system design?

To size the electrical disconnect
To calculate pipe wall thickness
To determine how much heat the evaporator can absorb per kilogram of refrigerant (Correct answer)
To determine the colour code for refrigerant cylinders

Correct answer: To determine how much heat the evaporator can absorb per kilogram of refrigerant

The refrigeration effect (kJ/kg) tells the designer how much heat each kilogram of refrigerant absorbs as it passes through the evaporator, which is used to size the system for the required cooling load.

Question 25: What is a solenoid valve used for in the liquid line of a refrigeration system?

To prevent refrigerant backflow from the condenser to the compressor during shutdown
To regulate superheat at the evaporator outlet
To modulate liquid refrigerant flow continuously based on cooling demand
To open or close the liquid line fully in response to an electrical signal, controlling refrigerant flow on-off for pumpdown or zone control (Correct answer)

Correct answer: To open or close the liquid line fully in response to an electrical signal, controlling refrigerant flow on-off for pumpdown or zone control

A liquid line solenoid valve is an electrically actuated on-off valve that opens to allow refrigerant flow when the system calls for cooling and closes to stop flow, commonly used in pumpdown control cycles or multi-zone systems.

Question 26: What is sensible heat?

Heat that changes the temperature of a substance without changing its phase (Correct answer)
Heat that cannot be detected by instruments
Heat stored in the refrigerant's pressure
Heat transferred only by radiation

Correct answer: Heat that changes the temperature of a substance without changing its phase

Sensible heat is heat energy that causes a measurable temperature change in a substance without changing its physical state.

Question 27: What is the purpose of a suction line filter-drier?

To remove moisture and debris from the suction line, protecting the compressor from acid, moisture, and particulates after a compressor burnout (Correct answer)
To superheat the suction vapour to prevent liquid slugging
To separate oil from the suction vapour before it enters the compressor
To reduce suction line pressure drop to increase system efficiency

Correct answer: To remove moisture and debris from the suction line, protecting the compressor from acid, moisture, and particulates after a compressor burnout

A suction line filter-drier is typically installed after a compressor burnout to remove acid, moisture, and carbon deposits from the refrigerant before they can damage the replacement compressor.

Question 28: What causes frost to build up on an evaporator coil in a refrigeration system?

Refrigerant overcharge causing the coil surface to reach 0°C or below, and moisture in the air freezing on the coil (Correct answer)
Oil logging in the coil reducing refrigerant flow
High superheat causing dry spots on the coil surface
Low head pressure reducing the heat transfer rate

Correct answer: Refrigerant overcharge causing the coil surface to reach 0°C or below, and moisture in the air freezing on the coil

When the evaporator coil surface temperature falls to 0°C or below, moisture from the air passing over the coil freezes and accumulates as frost, which insulates the coil and reduces heat transfer.

Question 29: What is the purpose of a liquid receiver in a refrigeration system?

To separate oil from the refrigerant
To filter moisture from the refrigerant
To store liquid refrigerant and ensure a steady supply to the expansion device (Correct answer)
To measure refrigerant charge by weight

Correct answer: To store liquid refrigerant and ensure a steady supply to the expansion device

A liquid receiver stores a reserve of liquid refrigerant on the high side of the system, ensuring a continuous and bubble-free supply of liquid to the expansion device under varying load conditions.

Question 30: What is the purpose of a crankcase pressure regulator (CPR) valve?

To regulate oil pressure in the crankcase
To limit the suction pressure entering the compressor during pulldown or hot gas defrost to prevent motor overload (Correct answer)
To regulate discharge pressure
To control the crankcase heater

Correct answer: To limit the suction pressure entering the compressor during pulldown or hot gas defrost to prevent motor overload

A CPR valve is installed in the suction line to throttle suction gas and prevent the compressor from seeing excessive suction pressure during pulldown after defrost or startup of a warm system. High suction pressure causes high current draw that can trip overloads or damage the motor. The CPR gradually allows full pressure as the system cools down.

Question 31: What is the purpose of a relief valve on a refrigeration pressure vessel under CSA B52?

To release refrigerant to the atmosphere to reduce system charge during overcharge conditions
To balance pressure between the high and low sides of the system during shutdown
To manually release pressure before opening the system for service
To automatically vent refrigerant if internal pressure exceeds a safe limit, preventing catastrophic vessel rupture (Correct answer)

Correct answer: To automatically vent refrigerant if internal pressure exceeds a safe limit, preventing catastrophic vessel rupture

A relief valve is a code-required safety device that automatically opens to release refrigerant when vessel pressure exceeds the design limit, preventing a potentially catastrophic mechanical failure of the pressure vessel.

Question 32: What does a ground fault circuit interrupter (GFCI) protect against in HVAC applications?

Electrical shock by detecting small leakage currents (as low as 5 mA) to ground and opening the circuit within milliseconds (Correct answer)
Motor overloads that would cause winding overheating
Short circuits in the compressor motor windings
Voltage sags that could damage sensitive electronic controls

Correct answer: Electrical shock by detecting small leakage currents (as low as 5 mA) to ground and opening the circuit within milliseconds

A GFCI monitors the difference between current on the hot and neutral conductors; if even a small current (≥5 mA) is flowing to ground through a person or fault path, it trips in about 25 milliseconds, preventing lethal electric shock.

Question 33: What is the purpose of a pressure-limiting TXV (also called a 'maximum operating pressure' or MOP TXV)?

To prevent evaporator pressure from rising above a set point during high-load conditions, protecting the compressor motor from overload (Correct answer)
To prevent the evaporator coil from reaching freezing temperatures in low-ambient conditions
To limit refrigerant flow during initial system startup
To limit the maximum pressure on the high side of the system

Correct answer: To prevent evaporator pressure from rising above a set point during high-load conditions, protecting the compressor motor from overload

A MOP TXV has a built-in feature that limits the maximum suction pressure (and therefore evaporator temperature) to protect the compressor motor from drawing excessive current during pulldown of a warm load.

Question 34: What is a scroll compressor and what are its advantages?

A compressor using a piston and cylinder; advantage is simplicity
A compressor using centrifugal force; advantage is very high capacity
A compressor using rotating vanes; advantage is high capacity
A compressor using two spiral-shaped scrolls (one fixed, one orbiting) that trap and compress gas; advantages include fewer moving parts, lower noise, and higher efficiency (Correct answer)

Correct answer: A compressor using two spiral-shaped scrolls (one fixed, one orbiting) that trap and compress gas; advantages include fewer moving parts, lower noise, and higher efficiency

A scroll compressor uses two interleaving spiral-shaped scrolls — one stationary and one orbiting. Gas is trapped between the scrolls and compressed as it moves toward the centre. Advantages include fewer moving parts (no valves), quieter operation, higher efficiency, and better tolerance of liquid slugging compared to reciprocating compressors.

Question 35: What is subcooling in the refrigeration cycle?

Reducing the refrigerant charge below recommended levels
Cooling the evaporator below 0°C
The temperature of the liquid refrigerant below its condensing (saturation) temperature at condenser pressure (Correct answer)
The temperature drop across the compressor

Correct answer: The temperature of the liquid refrigerant below its condensing (saturation) temperature at condenser pressure

Subcooling is the temperature difference between the actual liquid refrigerant temperature and its saturation temperature at condenser pressure. Adequate subcooling (typically 5°C to 10°C) ensures solid liquid reaches the metering device, improving system efficiency and indicating proper refrigerant charge.

Question 36: What does the SNAP (Significant New Alternatives Policy) program represent in the context of Canadian refrigerant regulations?

A Canadian federal program for approving new refrigerant alternatives
A U.S. EPA program that Canada references for guidance on acceptable refrigerant substitutes (Correct answer)
An industry association certification for refrigerant recovery technicians
A TSSA safety approval process for new refrigerant equipment

Correct answer: A U.S. EPA program that Canada references for guidance on acceptable refrigerant substitutes

SNAP is a U.S. EPA program listing acceptable and unacceptable substitutes for ODS; Canadian regulators and industry often reference SNAP listings when evaluating new refrigerant alternatives, though Canada's own ODSHAR is the binding regulation.

Question 37: What does enthalpy represent in refrigeration thermodynamics?

The total heat content of the refrigerant per unit mass (Correct answer)
The pressure drop across the expansion valve
The temperature difference between inlet and outlet of the condenser
The entropy change during compression

Correct answer: The total heat content of the refrigerant per unit mass

Enthalpy (kJ/kg) represents the total heat content of the refrigerant, including internal energy and flow work, and is used to calculate heat transfer in each component of the cycle.

Question 38: In Canadian HVAC wiring, what voltage is most commonly used for low-voltage control circuits?

24 V AC (Correct answer)
12 V DC
120 V AC
48 V AC

Correct answer: 24 V AC

24 V AC is the standard low-voltage control circuit voltage in Canadian and North American HVAC systems, provided by a step-down transformer from 120 V or 240 V.

Question 39: What is superheat in the refrigeration cycle and why is it important?

The temperature above the boiling point of the refrigerant vapour leaving the evaporator; it ensures no liquid enters the compressor (Correct answer)
The heat generated by the compressor motor
The maximum temperature the system can reach
The temperature difference between indoor and outdoor air

Correct answer: The temperature above the boiling point of the refrigerant vapour leaving the evaporator; it ensures no liquid enters the compressor

Superheat is the temperature of the refrigerant vapour above its saturation (boiling) temperature at a given pressure. Measuring superheat at the evaporator outlet ensures all liquid has evaporated and only vapour enters the compressor, preventing liquid slugging that can damage the compressor.

Question 40: In a three-phase motor connection, what is the difference between a wye (star) and delta configuration?

Wye is used only for single-phase motors; delta is only for three-phase motors
Wye connects each winding between a line and a neutral point; delta connects each winding directly between two lines, resulting in different voltage across each winding (Correct answer)
Wye and delta refer to the direction of motor rotation, not the winding configuration
Wye provides higher torque at startup; delta provides higher torque at full speed in all motors

Correct answer: Wye connects each winding between a line and a neutral point; delta connects each winding directly between two lines, resulting in different voltage across each winding

In a wye connection, one end of each winding meets at a neutral point and the other end connects to a line, so each winding sees line-to-neutral voltage; in a delta connection, each winding is connected line-to-line, so each winding sees full line voltage.

Question 41: Per the Canadian Refrigeration Code, what is the maximum recommended support spacing for horizontal copper refrigerant suction lines?

1.2 m (4 ft)
Support is only required at changes of direction
300 mm (12 in)
3 m (10 ft) (Correct answer)

Correct answer: 3 m (10 ft)

The Canadian Refrigeration Code and ASHRAE recommend maximum support intervals of approximately 3 m (10 ft) for copper refrigerant lines to prevent sagging, vibration fatigue, and stress on brazed joints.

Question 42: Under Canadian ODSHAR regulations, what must technicians do with recovered refrigerant that cannot be reused?

Mix it with new refrigerant to dilute contaminants
Return it to the original equipment manufacturer
Vent it outdoors in a remote location
Store it in an approved container and send it to a licensed refrigerant reclaimer or destruction facility (Correct answer)

Correct answer: Store it in an approved container and send it to a licensed refrigerant reclaimer or destruction facility

Intentional venting of controlled refrigerants is prohibited in Canada; recovered refrigerant that cannot be reused must be sent to a licensed reclaimer or destruction facility in approved containers.

Question 43: What is an electronic expansion valve (EEV) and what is its advantage over a TXV?

A valve controlled by a microprocessor and stepper motor that can respond faster and more precisely to changing load conditions than a thermostatic valve (Correct answer)
A valve with an electronic display for monitoring refrigerant flow rate
A valve that automatically detects the type of refrigerant and adjusts accordingly
A valve that uses electrical resistance heating to prevent ice formation on the valve body

Correct answer: A valve controlled by a microprocessor and stepper motor that can respond faster and more precisely to changing load conditions than a thermostatic valve

An EEV uses a stepper motor controlled by a microprocessor to precisely modulate refrigerant flow, offering faster response, greater precision, and compatibility with variable-speed systems compared to a mechanical TXV.

Question 44: What is the critical point of a refrigerant?

The lowest temperature at which the refrigerant remains liquid
The point at which refrigerant decomposes
The temperature and pressure above which no distinction exists between liquid and vapour phases (Correct answer)
The maximum operating pressure of the system

Correct answer: The temperature and pressure above which no distinction exists between liquid and vapour phases

The critical point is the specific temperature and pressure above which a refrigerant exists as a supercritical fluid and cannot be liquefied by pressure alone.

Question 45: What is a potential relay and what does it do in a compressor motor circuit?

A relay that detects power outages
A relay that switches between heating and cooling modes
A relay that controls the reversing valve
A relay that disconnects the start capacitor and/or start winding once the compressor motor reaches approximately 75% of its running speed, using the back-EMF voltage of the start winding (Correct answer)

Correct answer: A relay that disconnects the start capacitor and/or start winding once the compressor motor reaches approximately 75% of its running speed, using the back-EMF voltage of the start winding

A potential relay monitors the back-EMF (counter-electromotive force) voltage generated by the start winding as the motor accelerates. When this voltage reaches a threshold (typically at 75% of running speed), the relay opens its normally closed contacts, disconnecting the start capacitor from the circuit to prevent overheating and damage.

Question 46: What is the purpose of a distributor nozzle installed at the inlet of a multi-circuit evaporator?

To evenly distribute refrigerant flow to all circuits of the evaporator for uniform heat transfer (Correct answer)
To filter debris before refrigerant enters the evaporator circuits
To increase refrigerant pressure before entering the evaporator
To measure the mass flow rate of refrigerant entering the evaporator

Correct answer: To evenly distribute refrigerant flow to all circuits of the evaporator for uniform heat transfer

A distributor nozzle breaks the refrigerant into equal flows for each evaporator circuit, ensuring uniform distribution and preventing some circuits from starving while others flood.

Question 47: What is a standing pressure test and what does it verify?

Pressurizing the system with dry nitrogen to a specified pressure and monitoring for a drop over time to verify the system has no leaks (Correct answer)
A test of the compressor's discharge pressure during operation
A measurement of oil pressure in the compressor
A test of the water pressure in cooling towers

Correct answer: Pressurizing the system with dry nitrogen to a specified pressure and monitoring for a drop over time to verify the system has no leaks

A standing pressure test involves pressurizing the system with dry nitrogen (often with a trace of refrigerant for electronic leak detection) to the test pressure specified by the equipment manufacturer. The system is then isolated and monitored for a minimum of 24 hours. Any pressure drop indicates a leak that must be found and repaired.

Question 48: What is the purpose of a nitrogen purge when brazing refrigerant lines?

To prevent the flame from overheating the pipe by providing a cooling flow
To displace oxygen inside the pipe during brazing, preventing oxide scale formation inside the copper tube that would contaminate the refrigerant system (Correct answer)
To cool the braze joint faster to improve joint strength
To pressurize the system so leaks are visible as bubbles during brazing

Correct answer: To displace oxygen inside the pipe during brazing, preventing oxide scale formation inside the copper tube that would contaminate the refrigerant system

Flowing dry nitrogen through the tubing during brazing displaces oxygen inside the pipe, preventing the formation of copper oxide scale (cupric oxide) that would otherwise flake off and contaminate the compressor valves and expansion devices.

Question 49: What does an electronic leak detector indicate when it sounds an alarm near a refrigerant line?

High refrigerant velocity in the pipe indicating a restriction
Presence of moisture in the refrigerant circuit
Electrical fault in the refrigerant circuit wiring
Detection of refrigerant vapour concentration above the instrument's threshold at that location (Correct answer)

Correct answer: Detection of refrigerant vapour concentration above the instrument's threshold at that location

An electronic leak detector senses refrigerant vapour concentration and alarms when it exceeds the instrument's sensitivity threshold, indicating a likely leak source that the technician should confirm and repair.

Question 50: What is the purpose of the equalizer line on an externally equalized TXV?

To sense evaporator outlet pressure at the TXV diaphragm, compensating for pressure drop across the evaporator for accurate superheat control (Correct answer)
To add refrigerant charge to the system remotely
To drain condensate from the evaporator drain pan
To equalize refrigerant pressure between the high and low side during the off-cycle

Correct answer: To sense evaporator outlet pressure at the TXV diaphragm, compensating for pressure drop across the evaporator for accurate superheat control

An external equalizer connects the TXV diaphragm case to the evaporator outlet, so the valve responds to the actual evaporator outlet pressure rather than the inlet pressure, compensating for pressure drop across the evaporator and maintaining accurate superheat control.

Question 51: What is a thermostatic expansion valve (TXV/TEV) and how does it operate?

A valve that controls water flow through the condenser
A valve that modulates refrigerant flow based on the superheat at the evaporator outlet, using a sensing bulb, equalizer, and spring (Correct answer)
A valve that opens and closes based on time
A valve that responds to room temperature

Correct answer: A valve that modulates refrigerant flow based on the superheat at the evaporator outlet, using a sensing bulb, equalizer, and spring

A TXV/TEV modulates refrigerant flow to maintain a constant superheat at the evaporator outlet. It uses three forces: the sensing bulb pressure (opening force, responds to suction line temperature), the equalizer pressure (closing force, responds to evaporator pressure), and the spring pressure (closing force, sets superheat).

Question 52: Which type of mechanical fitting is preferred for refrigerant piping connections that must be disassembled for service?

SAE 45° flare fittings (Correct answer)
Press-fit (crimped) copper fittings
Compression fittings
Socket-type brazed fittings

Correct answer: SAE 45° flare fittings

SAE 45° flare fittings are designed for repeated field disassembly and reassembly and are the standard choice wherever a serviceable mechanical joint is required, such as at service valves and gauge ports.

Question 53: What is subcooling in a refrigeration system?

The number of degrees the liquid refrigerant is cooled below its condensing temperature (Correct answer)
Cooling the suction line below ambient temperature
Lowering evaporator pressure below design
Reducing compressor speed below design RPM

Correct answer: The number of degrees the liquid refrigerant is cooled below its condensing temperature

Subcooling refers to cooling the liquid refrigerant below its saturation temperature at the condenser outlet, which prevents flash gas in the liquid line and improves system efficiency.

Question 54: What damage can liquid slugging cause to a reciprocating compressor?

It improves compressor efficiency
It can break valves, connecting rods, and the crankshaft because liquids are incompressible (Correct answer)
It only causes minor noise issues
It causes the motor to overheat

Correct answer: It can break valves, connecting rods, and the crankshaft because liquids are incompressible

Liquid slugging occurs when liquid refrigerant or oil enters the compressor cylinder. Since liquids are essentially incompressible, the compressor attempts to compress an incompressible fluid, resulting in extreme pressures that can break reed valves, bend connecting rods, crack pistons, and damage the crankshaft.

Question 55: What is a direct expansion (DX) evaporator?

An evaporator that uses hot water for heating
An evaporator that uses a secondary coolant like glycol
An evaporator with no fins
An evaporator where refrigerant expands directly inside the coil to cool air or fluid passing over or around it, with the metering device controlling flow (Correct answer)

Correct answer: An evaporator where refrigerant expands directly inside the coil to cool air or fluid passing over or around it, with the metering device controlling flow

A direct expansion (DX) evaporator is the most common type in residential and commercial HVAC. Refrigerant from the metering device expands directly inside the evaporator tubes, absorbing heat from air passing over the finned coil. The metering device controls refrigerant flow to maintain proper superheat.

Question 56: What is the approach temperature of an air-cooled condenser?

The difference between condensing temperature and entering air temperature (Correct answer)
The difference between discharge temperature and condensing temperature
The temperature of the air at the condenser fan inlet
The difference between entering air temperature and leaving air temperature

Correct answer: The difference between condensing temperature and entering air temperature

Approach temperature is the difference between the condensing temperature (saturation temperature at condensing pressure) and the entering air dry-bulb temperature, and a low approach temperature indicates good heat transfer.

Question 57: What personal protective equipment (PPE) is mandatory when handling refrigerants under Canadian safety regulations?

Safety glasses or goggles and insulated gloves as a minimum; a face shield, chemical-resistant apron, and respiratory protection depending on the refrigerant and quantity (Correct answer)
Hard hat and steel-toed boots only
Hearing protection and fall arrest harness only
Flame-resistant clothing only, required for all refrigerants

Correct answer: Safety glasses or goggles and insulated gloves as a minimum; a face shield, chemical-resistant apron, and respiratory protection depending on the refrigerant and quantity

Canadian OHS regulations and manufacturer SDSs require at minimum safety glasses/goggles and chemical-resistant gloves when handling refrigerants; additional PPE such as face shields and respirators are required for larger quantities or toxic refrigerants like ammonia.

Question 58: What are the four main components of a basic vapour-compression refrigeration cycle?

Fan, coil, thermostat, ductwork
Compressor, condenser, expansion valve, evaporator (Correct answer)
Compressor, boiler, turbine, condenser
Pump, heater, cooler, filter

Correct answer: Compressor, condenser, expansion valve, evaporator

The four essential components of a vapour-compression refrigeration cycle are: compressor (raises pressure and temperature), condenser (rejects heat), expansion device/metering device (reduces pressure), and evaporator (absorbs heat). Refrigerant flows through these components in a continuous cycle.

Question 59: What is the purpose of a condenser fan cycling control?

To reduce noise during nighttime operation
To synchronize fan operation with the compressor
To maintain adequate head pressure during low ambient temperatures by cycling condenser fans on and off (Correct answer)
To increase airflow during peak cooling demand

Correct answer: To maintain adequate head pressure during low ambient temperatures by cycling condenser fans on and off

In cold weather, the condenser can reject too much heat, causing head pressure to drop too low for the metering device to function properly. Condenser fan cycling controls turn fans off or reduce their speed to maintain minimum head pressure, ensuring proper refrigerant flow and system operation.

Question 60: What instrument is used to measure refrigerant pressure at service valves on a refrigeration system?

A digital manifold gauge set (Correct answer)
A psychrometric chart
A megohmmeter
A clamp-on ammeter

Correct answer: A digital manifold gauge set

A manifold gauge set (or digital manifold) connects to the high- and low-side service valves to measure suction and discharge pressures, allowing the technician to diagnose system performance and charge level.

Question 61: What is the function of the condenser in a refrigeration system?

To expand the refrigerant from high to low pressure
To reject heat from the refrigerant to the ambient medium, condensing the refrigerant from vapour to liquid (Correct answer)
To separate oil from refrigerant vapour
To filter moisture and debris from the refrigerant

Correct answer: To reject heat from the refrigerant to the ambient medium, condensing the refrigerant from vapour to liquid

The condenser rejects the heat absorbed in the evaporator plus the heat of compression to the outdoor air or cooling water, condensing the refrigerant vapour back into a liquid.

Question 62: What is the purpose of a lockout-tagout (LOTO) procedure when servicing HVAC equipment in Canada?

To seal the refrigerant circuit to prevent leaks during transport
To record service work completed on a tag attached to the equipment
To lock the thermostat at a fixed temperature to prevent tampering during service
To isolate and lock all energy sources (electrical, refrigerant pressure, etc.) to prevent unexpected re-energization during maintenance, protecting the technician from injury (Correct answer)

Correct answer: To isolate and lock all energy sources (electrical, refrigerant pressure, etc.) to prevent unexpected re-energization during maintenance, protecting the technician from injury

LOTO procedures, required under provincial occupational health and safety (OHS) regulations across Canada, ensure that electrical power and other energy sources are isolated and locked before service work begins, preventing accidental startup.

Question 63: What is the ozone depletion potential (ODP) of R-22 (HCFC-22)?

0.05
0.034 (Correct answer)
1.0
0

Correct answer: 0.034

R-22 has an ODP of 0.034 relative to R-11 (ODP=1.0), meaning it depletes the ozone layer but significantly less than the fully halogenated CFCs it replaced.

Question 64: What is the purpose of a discharge muffler on a refrigeration compressor?

To reduce refrigerant velocity and separate oil from the discharge gas
To cool the discharge gas before it enters the condenser
To act as a check valve preventing reverse flow into the compressor
To dampen pressure pulsations in the discharge line, reducing vibration and noise (Correct answer)

Correct answer: To dampen pressure pulsations in the discharge line, reducing vibration and noise

A discharge muffler attenuates the pressure pulsations generated by the reciprocating piston action, reducing vibration, noise, and potential stress on discharge line piping.

Question 65: On a pressure-enthalpy (P-h) diagram, what does the area under the saturation dome represent?

The critical point only
The subcooled liquid region
The two-phase (liquid-vapour) mixture region (Correct answer)
The superheated vapour region

Correct answer: The two-phase (liquid-vapour) mixture region

The area under the saturation dome on a P-h diagram represents the two-phase region where both liquid and vapour coexist at saturation conditions.

Question 66: What symptom would a restricted liquid line filter-drier produce in a refrigeration system?

High suction pressure and low superheat
Low suction pressure, high superheat, subcooling drop across the drier, and possibly a cold or frosted drier body (Correct answer)
High discharge pressure and normal suction pressure
Oil logging in the evaporator coil

Correct answer: Low suction pressure, high superheat, subcooling drop across the drier, and possibly a cold or frosted drier body

A restricted filter-drier creates a pressure drop across it, starving the expansion device of liquid — the result is low suction pressure, high superheat, a measurable subcooling temperature drop across the drier, and possibly frost on the drier body where pressure drops sharply.

Question 67: What is the function of a contactor in an HVAC system?

To protect against lightning strikes
An electrically operated switch that uses a low-voltage control signal to engage high-voltage power to the compressor and condenser fan motors (Correct answer)
To convert AC power to DC
To measure voltage

Correct answer: An electrically operated switch that uses a low-voltage control signal to engage high-voltage power to the compressor and condenser fan motors

A contactor is an electrically operated switch controlled by the thermostat's low-voltage signal (typically 24V AC). When the thermostat calls for cooling or heating, the contactor coil energizes, pulling in the contacts to connect high-voltage power (240V) to the compressor and outdoor fan motor.

Question 68: What is the purpose of the 'refrigerant log' required under Canadian ODSHAR for large systems?

To record technician certifications for each service visit
To record the brand name and purchase cost of refrigerant
To log the daily operating temperatures of the system
To document all refrigerant additions, removals, and leak checks to track charge losses over time (Correct answer)

Correct answer: To document all refrigerant additions, removals, and leak checks to track charge losses over time

ODSHAR requires operators of systems containing prescribed quantities of refrigerant to maintain a refrigerant log recording all additions, removals, and leak inspection results to demonstrate compliance with leak rate limits.

Question 69: What is the primary function of compressor oil in a refrigeration system?

To lubricate moving parts, seal clearances, and help cool the compressor motor (Correct answer)
To absorb moisture from the system
To increase the pressure of the refrigerant
To cool the refrigerant

Correct answer: To lubricate moving parts, seal clearances, and help cool the compressor motor

Compressor oil lubricates bearings, pistons, and other moving parts, seals the clearances between components to maintain compression efficiency, and helps dissipate heat from the motor windings. The oil must be compatible with the specific refrigerant used in the system.

Question 70: What is 'pumpdown control' in a refrigeration system?

A control strategy that closes the liquid line solenoid valve on system shutdown, allowing the compressor to pump refrigerant out of the low side into the receiver before stopping (Correct answer)
A procedure to manually remove all refrigerant from the system into a recovery cylinder
A startup procedure that pre-charges the evaporator before the compressor starts
A method of reducing system capacity by pumping refrigerant to a parallel circuit

Correct answer: A control strategy that closes the liquid line solenoid valve on system shutdown, allowing the compressor to pump refrigerant out of the low side into the receiver before stopping

Pumpdown control closes the liquid line solenoid on a call to stop cooling, and the compressor continues to run until suction pressure drops to a low-pressure cutout, drawing refrigerant out of the low side into the receiver to prevent migration during the off-cycle.

Question 71: What is the purpose of a thermostatic expansion valve (TXV)?

To control compressor discharge pressure
To regulate condenser fan speed based on outdoor temperature
To meter the flow of liquid refrigerant into the evaporator by maintaining a constant superheat at the evaporator outlet (Correct answer)
To bypass refrigerant around the compressor during startup

Correct answer: To meter the flow of liquid refrigerant into the evaporator by maintaining a constant superheat at the evaporator outlet

A TXV senses the superheat at the evaporator outlet and modulates the valve opening to maintain a near-constant superheat, ensuring the evaporator is fully utilized while protecting the compressor from liquid slugging.

Question 72: What is a pressure-enthalpy (P-h) diagram used for in HVAC?

To size electrical circuits for equipment
To measure duct pressure losses
To calculate building heat loads
To graphically represent the refrigeration cycle, showing the state of the refrigerant at each point and the energy involved in each process (Correct answer)

Correct answer: To graphically represent the refrigeration cycle, showing the state of the refrigerant at each point and the energy involved in each process

A pressure-enthalpy (P-h) diagram plots refrigerant pressure on the vertical axis and enthalpy (heat content) on the horizontal axis. It shows the saturation curve, the state of the refrigerant at each point in the cycle, and allows calculation of system capacity, COP, and heat transfer at each component.

Question 73: What is the relationship between pressure and boiling point of a refrigerant?

As pressure increases, the boiling point increases; as pressure decreases, the boiling point decreases (Correct answer)
As pressure increases, the boiling point decreases
They are unrelated
The boiling point is always constant regardless of pressure

Correct answer: As pressure increases, the boiling point increases; as pressure decreases, the boiling point decreases

The boiling point of a refrigerant is directly related to its pressure. This principle is fundamental to refrigeration: the low-pressure side allows the refrigerant to boil at a low temperature (absorbing heat), while the high-pressure side forces it to condense at a higher temperature (rejecting heat).

Question 74: What is an evaporative condenser and what is its primary advantage?

A condenser that operates on the principle of the Peltier effect; it has no moving parts
A condenser that rejects heat by spraying water over coils while air passes over them; it achieves lower condensing temperatures than air-cooled units (Correct answer)
A condenser that uses evaporating refrigerant internally to cool a second refrigerant circuit; it eliminates the need for a cooling tower
A condenser cooled by ice water from a thermal storage tank; it reduces peak electrical demand

Correct answer: A condenser that rejects heat by spraying water over coils while air passes over them; it achieves lower condensing temperatures than air-cooled units

An evaporative condenser sprays water over refrigerant coils while a fan draws air through; the evaporation of the water provides much more cooling than dry air alone, allowing lower condensing temperatures and higher system efficiency.

Question 75: What is the purpose of a crankcase heater on a compressor?

To keep the compressor oil warm during off cycles, preventing refrigerant migration and liquid slugging on startup (Correct answer)
To defrost the outdoor coil
To preheat the supply air
To warm the refrigerant for faster startup

Correct answer: To keep the compressor oil warm during off cycles, preventing refrigerant migration and liquid slugging on startup

A crankcase heater keeps the oil sump warm when the compressor is off. Without it, refrigerant can migrate to the cold compressor crankcase and mix with the oil. On startup, the sudden pressure drop would cause the liquid refrigerant to flash to vapour (foam), washing oil off bearings and causing potential liquid slugging.

Question 76: What is the main advantage of a scroll compressor over a reciprocating compressor?

Ability to handle liquid slugging without damage
Higher compression ratios suitable for industrial refrigeration
Lower initial purchase cost
Fewer moving parts, quieter operation, and higher efficiency at part load (Correct answer)

Correct answer: Fewer moving parts, quieter operation, and higher efficiency at part load

Scroll compressors have fewer moving parts than reciprocating compressors, resulting in smoother, quieter operation and generally higher energy efficiency, particularly at part-load conditions.

Question 77: What is the purpose of evacuating a refrigeration system and what vacuum level should be achieved?

Evacuation removes air and moisture by pulling a deep vacuum; target is 500 microns (0.5 mm Hg) or lower for systems using hygroscopic refrigerants like R-410A (Correct answer)
Evacuation removes oil; target is atmospheric pressure
Evacuation is optional if the system is new
Evacuation removes excess refrigerant; target is 0 psig

Correct answer: Evacuation removes air and moisture by pulling a deep vacuum; target is 500 microns (0.5 mm Hg) or lower for systems using hygroscopic refrigerants like R-410A

Evacuation uses a vacuum pump to remove non-condensable gases (air) and moisture from a refrigeration system. Air reduces efficiency and raises head pressure, while moisture causes acid formation, corrosion, and freeze-ups. A target of 500 microns or lower is standard for R-410A systems, held for at least 15-30 minutes to confirm a tight system.

Question 78: A compressor is running but suction pressure is very high and the system is not cooling. The discharge line is not hot. What is the most likely cause?

Failed compressor discharge or suction valves, causing the compressor to pump poorly (Correct answer)
Dirty condenser coil blocking heat rejection
A failed TXV stuck in the open position
Refrigerant overcharge causing high suction pressure

Correct answer: Failed compressor discharge or suction valves, causing the compressor to pump poorly

If the compressor is running but the discharge line is not hot and suction pressure is very high, the compressor valves have likely failed — the compressor is spinning but not effectively compressing the refrigerant, so it is not moving refrigerant through the system.

Question 79: What is the function of a low-pressure safety switch in a refrigeration system?

To control the expansion valve opening
To shut off the compressor if suction pressure drops too low, protecting against loss of charge, restricted airflow, or blocked metering device (Correct answer)
To start the compressor when pressure builds up
To maintain minimum suction pressure for efficiency

Correct answer: To shut off the compressor if suction pressure drops too low, protecting against loss of charge, restricted airflow, or blocked metering device

The low-pressure cutout protects the compressor by shutting it off when suction pressure drops below a safe minimum. Low suction pressure can result from refrigerant loss, restricted airflow (dirty filter/iced coil), blocked metering device, or faulty indoor fan. Operating at very low suction pressure can cause motor overheating and oil return problems.

Question 80: What is the maximum allowable refrigerant leak rate under Canadian ODSHAR for commercial refrigeration systems containing more than 10 kg of refrigerant?

5% of total charge per year
35% of total charge per year, with required repair within 30 days of detection (Correct answer)
There is no defined leak rate limit, only a mandatory repair timeline
10% of total charge per year

Correct answer: 35% of total charge per year, with required repair within 30 days of detection

Under ODSHAR, systems with more than 10 kg of refrigerant that leak 35% or more of their charge in a 12-month period trigger mandatory reporting and repair requirements.

Question 81: Why is it important to keep condenser coils clean?

Dirty coils have no significant impact on performance
Clean coils only affect noise levels
Dirty coils increase head pressure, reduce system capacity, increase energy consumption, and can cause compressor overheating and failure (Correct answer)
Clean coils look more professional

Correct answer: Dirty coils increase head pressure, reduce system capacity, increase energy consumption, and can cause compressor overheating and failure

Dirty condenser coils restrict airflow and insulate the heat transfer surface, causing the system to operate at higher head pressures. This increases compressor energy consumption, reduces cooling capacity, raises discharge temperatures (risking compressor damage), and shortens equipment life. Regular cleaning is essential preventive maintenance.

Question 82: Under the Canadian Environmental Protection Act (CEPA), which federal regulation specifically controls ozone-depleting substances (ODS) in Canada?

The Ozone-depleting Substances and Halocarbon Alternatives Regulations (ODSHAR) (Correct answer)
The Greenhouse Gas Pollution Pricing Act
The Montreal Protocol Domestic Implementation Act
The Refrigerant Management Canada Regulation

Correct answer: The Ozone-depleting Substances and Halocarbon Alternatives Regulations (ODSHAR)

The Ozone-depleting Substances and Halocarbon Alternatives Regulations (ODSHAR) under CEPA govern the use, import, export, and disposal of ODS and their alternatives in Canada.

Question 83: What is flash gas and how does it affect metering device performance?

The initial burst of gas when a system starts up
Refrigerant vapour that forms prematurely in the liquid line before reaching the metering device due to pressure drop or insufficient subcooling, reducing metering device capacity (Correct answer)
Gas produced by a flashlight leak detector
Gas used to flush a system clean

Correct answer: Refrigerant vapour that forms prematurely in the liquid line before reaching the metering device due to pressure drop or insufficient subcooling, reducing metering device capacity

Flash gas forms when liquid refrigerant partially vaporizes in the liquid line before reaching the metering device, caused by excessive pressure drop, insufficient subcooling, or a long vertical liquid line rise. Flash gas occupies space in the metering device, reducing the flow of actual liquid refrigerant and diminishing system capacity.

Question 84: When brazing copper-to-copper refrigerant joints, which brazing alloy is most commonly specified?

BCuP-5 (15% silver, copper-phosphorus) (Correct answer)
BAg-7 (56% silver)
Soft solder (50/50 tin-lead)
BCuP-2 (copper-phosphorus, no silver)

Correct answer: BCuP-5 (15% silver, copper-phosphorus)

BCuP-5 (15% silver) is the industry standard for copper-to-copper refrigerant joints because it is self-fluxing on copper and flows reliably at brazing temperatures.

Question 85: What are the dangers of mixing different refrigerants in a system?

Different refrigerants naturally separate and cause no issues
Mixing is recommended for better performance
It only causes a slight reduction in efficiency
It can create unpredictable pressures, reduce capacity, damage the compressor, void equipment warranties, and create unsafe operating conditions (Correct answer)

Correct answer: It can create unpredictable pressures, reduce capacity, damage the compressor, void equipment warranties, and create unsafe operating conditions

Mixing refrigerants creates an unknown blend with unpredictable pressure-temperature characteristics, potentially causing dangerously high pressures, compressor damage from oil compatibility issues, reduced capacity, and voided warranties. Mixed refrigerants cannot be recycled or reclaimed and must be destroyed. This is why recovery cylinders are dedicated to specific refrigerants.

Question 86: Why is adequate airflow across an evaporator coil critical for proper system operation?

It prevents frost formation at any operating temperature
It ensures sufficient heat transfer to vaporize the refrigerant and maintain proper suction pressure and superheat (Correct answer)
It prevents refrigerant from changing phase inside the coil
It is required to lubricate the TXV sensing bulb

Correct answer: It ensures sufficient heat transfer to vaporize the refrigerant and maintain proper suction pressure and superheat

Adequate airflow ensures the evaporator coil receives enough heat from the space to fully evaporate the refrigerant; insufficient airflow reduces heat transfer, dropping suction pressure and causing the coil to ice up.

Question 87: What is the unit of heat energy used in Canadian HVAC calculations?

Calorie
Joule (J) or kilojoule (kJ) (Correct answer)
Foot-pound
BTU

Correct answer: Joule (J) or kilojoule (kJ)

Canada uses SI (metric) units, so heat energy is measured in joules (J) or kilojoules (kJ) in accordance with Canadian standards.

Question 88: What is the proper method for charging R-410A refrigerant into a system?

Charge as a gas through the suction side only
Charge as a liquid through the high side (liquid line) or through the suction side with a metering device to prevent liquid slugging, because R-410A is a near-azeotropic blend (Correct answer)
Charge as a gas through the discharge side
Charge by weight through the compressor oil port

Correct answer: Charge as a liquid through the high side (liquid line) or through the suction side with a metering device to prevent liquid slugging, because R-410A is a near-azeotropic blend

R-410A is a near-azeotropic blend (R-32/R-125) that must be charged as a liquid to maintain the correct composition. Liquid can be charged through the liquid line directly or through the suction side using a restrictor to flash the liquid to vapour before it enters the compressor. The cylinder must be inverted or use a dip tube.

Question 89: Which flux is required when brazing copper tubing to a brass or steel fitting?

A proper brazing flux (AWS Type FB3-A or equivalent) must be applied (Correct answer)
Flux is only required when using oxygen-acetylene equipment
Standard paste solder flux is sufficient
No flux is needed on any copper joint

Correct answer: A proper brazing flux (AWS Type FB3-A or equivalent) must be applied

BCuP alloys are self-fluxing only on copper-to-copper joints; when joining copper to brass or steel, a dedicated brazing flux must be used to prevent oxidation and ensure proper flow.

Question 90: Which refrigerant leak detection method offers the highest sensitivity, capable of detecting leaks as small as 0.1 oz per year?

Bubble solution (soap) test
Electronic refrigerant leak detector (Correct answer)
Nitrogen standing pressure test
UV fluorescent dye and black light

Correct answer: Electronic refrigerant leak detector

Electronic leak detectors (heated diode, infrared, or heated pentode types) are capable of detecting trace levels of refrigerant far below the threshold of bubble or UV dye methods.

Question 91: What is a 'pressure test' as performed under CSA B52 after installing a new refrigeration system?

Measuring suction and discharge pressures with a manifold gauge after startup
Pressurizing the system with dry nitrogen to the test pressure specified in CSA B52 to verify the integrity of the refrigerant circuit before introducing refrigerant (Correct answer)
Pressurizing the system with refrigerant to operating pressure to check for leaks
Testing the relief valve by manually lifting it at operating pressure

Correct answer: Pressurizing the system with dry nitrogen to the test pressure specified in CSA B52 to verify the integrity of the refrigerant circuit before introducing refrigerant

CSA B52 requires a pressure test using dry nitrogen (never oxygen or refrigerant alone) to a specified test pressure before refrigerant is introduced, verifying that all joints, fittings, and components are leak-free and structurally sound.

Question 92: What is a transformer in an HVAC control circuit and what voltage does it typically provide?

It steps down line voltage (240V or 120V) to 24V AC to power the thermostat and control circuit safely (Correct answer)
It converts AC to DC for electronic controls
It converts 24V to 240V for the compressor
It boosts voltage during brown-out conditions

Correct answer: It steps down line voltage (240V or 120V) to 24V AC to power the thermostat and control circuit safely

The control transformer in an HVAC system steps down the line voltage (typically 240V or 120V) to 24V AC. This low voltage safely powers the thermostat, control relays, and safety switches. The transformer is usually located in the air handler or furnace and is protected by a fuse on the secondary (24V) side.

Question 93: What is the coefficient of performance (COP) of a refrigeration system?

The ratio of refrigeration effect to the work input to the compressor (Correct answer)
The ratio of heat rejected at the condenser to work input
The ratio of compressor discharge pressure to suction pressure
The ratio of evaporator temperature to condenser temperature in Kelvin

Correct answer: The ratio of refrigeration effect to the work input to the compressor

COP is defined as the useful refrigeration effect (heat absorbed at the evaporator) divided by the compressor work input, indicating system efficiency.

Question 94: What is the purpose of a contactor in an HVAC electrical circuit?

To protect against ground faults in the power supply
To measure and display voltage and current to the compressor
To act as an electrically operated switch that uses a low-voltage control coil to open and close high-voltage power contacts to the compressor or fan motor (Correct answer)
To convert single-phase power to three-phase power for the compressor

Correct answer: To act as an electrically operated switch that uses a low-voltage control coil to open and close high-voltage power contacts to the compressor or fan motor

A contactor uses a low-voltage coil (typically 24V) energized by the control circuit to magnetically close heavy-duty power contacts, allowing full line voltage to energize loads like compressors and fan motors.

Question 95: In the vapour-compression refrigeration cycle, at which component does the refrigerant absorb heat from the space being cooled?

Compressor
Condenser
Expansion valve
Evaporator (Correct answer)

Correct answer: Evaporator

The evaporator is where the low-pressure liquid refrigerant boils and absorbs latent heat from the surrounding space, providing the cooling effect.

Question 96: What is a current sensing relay and where is it used?

A relay that senses the current in the thermostat wire
A relay that monitors compressor motor current draw to disconnect the start winding; used primarily in fractional-horsepower compressors (Correct answer)
A relay used in variable-speed drives
A relay that measures current in the defrost heater

Correct answer: A relay that monitors compressor motor current draw to disconnect the start winding; used primarily in fractional-horsepower compressors

A current sensing relay uses the compressor motor's running current to control the start winding circuit. At startup, high locked-rotor current keeps the relay's contacts closed, energizing the start winding. As the motor reaches speed and current drops, the relay opens, disconnecting the start circuit. It is used in small, fractional-HP compressors.

Question 97: What is the role of the unloader on a compressor?

To reduce compressor capacity by holding suction valves open on selected cylinders so they do not pump (Correct answer)
To disengage the motor from the compressor shaft during startup
To release excess refrigerant charge back to the low side during overcharge conditions
To open a bypass around the condenser to reduce head pressure

Correct answer: To reduce compressor capacity by holding suction valves open on selected cylinders so they do not pump

A compressor unloader mechanism holds suction valves open on one or more cylinders so those cylinders do no useful compression work, effectively reducing the compressor's pumping capacity to match lower load conditions.

Question 98: What is the recommended method to confirm a refrigerant leak location after an electronic detector gives an alarm?

Replace all brazed joints in the area indicated by the detector
Pressurize the system above normal operating pressure to make the leak larger and easier to find
Open the system immediately and visually inspect all joints
Apply an approved refrigerant-compatible leak detection solution (bubble solution) or use a UV dye and UV light to pinpoint the exact leak location (Correct answer)

Correct answer: Apply an approved refrigerant-compatible leak detection solution (bubble solution) or use a UV dye and UV light to pinpoint the exact leak location

After an electronic detector alerts to a possible leak, bubble solution or UV dye with a UV lamp is used to pinpoint the exact location; UV dye that was pre-charged into the system glows brightly at the leak site under UV light.

Question 99: Why must oxygen (O2) never be used to pressure test a refrigeration system?

Oxygen is too expensive for routine use as a test gas
Oxygen reacts with refrigerant oils to form an explosive mixture that can detonate under pressure (Correct answer)
Oxygen dissolves into the refrigerant and changes its thermodynamic properties
Oxygen is a non-condensable that is difficult to purge from the system after testing

Correct answer: Oxygen reacts with refrigerant oils to form an explosive mixture that can detonate under pressure

Oxygen mixed with refrigerant oil vapour under pressure creates a potentially explosive mixture — this hazard has caused fatal accidents, and all codes absolutely prohibit using oxygen or air to pressure test refrigeration systems.

Question 100: What is 'compressor short cycling' and what are its main causes?

Rapid and repeated on-off cycling of the compressor; caused by oversized equipment, low refrigerant charge, or faulty controls (Correct answer)
A compressor running continuously at full load without cycling off; caused by undersized equipment
A compressor bypassing the suction valve; caused by worn valve reeds
Running two compressors in parallel when only one is needed; caused by faulty staging controls

Correct answer: Rapid and repeated on-off cycling of the compressor; caused by oversized equipment, low refrigerant charge, or faulty controls

Short cycling refers to the compressor turning on and off too frequently, which stresses motors and bearings; common causes include oversized systems that quickly satisfy the setpoint, low refrigerant charge, or faulty pressure controls.

Question 101: What is the GWP (Global Warming Potential) of R-410A and why is this significant for the Canadian HVAC industry?

GWP of approximately 2,088; it is being phased down under the Kigali Amendment and Canadian HFC regulations, requiring transition to lower-GWP alternatives (Correct answer)
GWP of 1; it has no environmental impact
GWP of 10; it is considered low impact
GWP of 100; it is only significant in industrial applications

Correct answer: GWP of approximately 2,088; it is being phased down under the Kigali Amendment and Canadian HFC regulations, requiring transition to lower-GWP alternatives

R-410A has a GWP of approximately 2,088 (meaning it traps 2,088 times more heat than CO₂ over 100 years). Canada has ratified the Kigali Amendment to phase down HFC production and consumption. The HVAC industry is transitioning to lower-GWP alternatives like R-32 (GWP 675) and R-454B (GWP 466) in new equipment.

Question 102: What is the 'head pressure control' strategy used on air-cooled condensers in cold Canadian winters?

Increasing compressor speed to compensate for low ambient temperature
Opening the bypass valve to route refrigerant around the condenser
Cycling condenser fans off or modulating fan speed to maintain minimum condensing pressure during cold weather (Correct answer)
Reducing refrigerant charge to lower head pressure

Correct answer: Cycling condenser fans off or modulating fan speed to maintain minimum condensing pressure during cold weather

In cold weather, air-cooled condensers can overcool the refrigerant and reduce condensing pressure below the minimum needed for proper expansion device operation, so fan cycling or variable-speed fans maintain minimum head pressure.

Question 103: In the refrigeration cycle, what state change does the refrigerant undergo in the evaporator?

Gas to solid (deposition)
Gas to liquid (condensation)
Solid to liquid (melting)
Liquid to gas (evaporation/boiling) (Correct answer)

Correct answer: Liquid to gas (evaporation/boiling)

In the evaporator, low-pressure liquid refrigerant absorbs heat from the space being cooled and changes state from liquid to gas (evaporation). This phase change absorbs a large amount of latent heat, which is what produces the cooling effect.

Question 104: What causes a TXV to hunt (oscillate)?

Improper sensing bulb placement, oversized valve, liquid in the suction line, or rapid load changes causing the valve to overcorrect repeatedly (Correct answer)
Low ambient temperature only
Normal operation
High refrigerant charge only

Correct answer: Improper sensing bulb placement, oversized valve, liquid in the suction line, or rapid load changes causing the valve to overcorrect repeatedly

TXV hunting is a condition where the valve repeatedly overcorrects — opening too wide then closing too much — causing oscillating superheat and unstable operation. Common causes include: poorly mounted sensing bulb, oversized valve, external equalizer problems, liquid slugging affecting the sensing bulb, or a system with rapidly changing loads.

Question 105: What is a thermostat and how does a programmable thermostat save energy?

A temperature-sensing control that activates heating or cooling; a programmable thermostat saves energy by automatically adjusting setpoints based on schedules (setback during unoccupied periods) (Correct answer)
A safety device that prevents overheating
A device that measures humidity only
A switch that only turns on heating

Correct answer: A temperature-sensing control that activates heating or cooling; a programmable thermostat saves energy by automatically adjusting setpoints based on schedules (setback during unoccupied periods)

A thermostat senses room temperature and signals the HVAC equipment to cycle on or off to maintain the setpoint. Programmable thermostats save energy by automatically reducing heating or increasing cooling setpoints during scheduled unoccupied or sleeping periods (setback/setup), reducing the temperature difference the system must maintain.

Question 106: What is the purpose of a time-delay relay (anti-short-cycle timer) in a compressor control circuit?

To delay the opening of the liquid line solenoid valve after the compressor starts
To sequence the startup of multiple refrigeration circuits to reduce electrical demand peaks
To time the duration of each defrost cycle precisely
To prevent the compressor from restarting immediately after shutdown, allowing pressures to equalize and protecting the motor from high-torque restarts (Correct answer)

Correct answer: To prevent the compressor from restarting immediately after shutdown, allowing pressures to equalize and protecting the motor from high-torque restarts

An anti-short-cycle timer prevents the compressor from restarting for a preset period (typically 3–5 minutes) after shutdown, allowing system pressures to equalize and protecting the motor from the strain of starting against high differential pressure.

Question 107: What is the function of a motor start capacitor in a single-phase PSC or CSIR compressor?

To improve the power factor of the motor during continuous running
To protect the motor windings from voltage spikes during starting
To store electrical charge for emergency compressor operation during power outages
To provide a phase-shifted current to the start winding to create a rotating magnetic field and initiate motor rotation (Correct answer)

Correct answer: To provide a phase-shifted current to the start winding to create a rotating magnetic field and initiate motor rotation

A start capacitor shifts the phase of the current in the start winding relative to the run winding, creating a rotating magnetic field that produces starting torque; it is switched out of the circuit once the motor reaches operating speed.

Question 108: A nitrogen standing pressure test is held at 200 psig. After 60 minutes the gauge reads 192 psig with no change in ambient temperature. What is the most likely explanation?

Normal absorption of nitrogen into the refrigeration oil
A leak exists somewhere in the system (Correct answer)
Nitrogen is condensing inside the tubing at operating temperature
The Bourdon gauge is reading low due to calibration drift

Correct answer: A leak exists somewhere in the system

Nitrogen does not condense or absorb into oil under normal conditions, so any measurable pressure drop during a standing test at constant temperature indicates a leak.

Question 109: What is the purpose of a defrost timer in a refrigeration system?

To delay compressor startup after a power interruption to prevent short cycling
To record the number of hours the compressor has operated for maintenance scheduling
To initiate defrost cycles at preset time intervals and terminate them after a set duration or when a termination thermostat trips (Correct answer)
To limit compressor run time per hour to prevent overheating

Correct answer: To initiate defrost cycles at preset time intervals and terminate them after a set duration or when a termination thermostat trips

A defrost timer initiates defrost at programmed intervals (e.g., every 6 or 8 hours) and terminates the defrost cycle when a time limit or defrost termination thermostat setpoint is reached, then returns the system to normal cooling.

Question 110: What is a hot gas defrost system?

A system that routes hot discharge gas from the compressor directly to the evaporator to melt accumulated frost (Correct answer)
A system that reverses airflow through the evaporator to remove frost by warm ambient air
A system that circulates warm glycol solution through the evaporator coil during defrost
A system that uses electric resistance heaters to melt frost from the evaporator coil

Correct answer: A system that routes hot discharge gas from the compressor directly to the evaporator to melt accumulated frost

Hot gas defrost bypasses normal refrigerant flow by directing hot compressor discharge gas into the evaporator coil, where its heat melts the frost accumulation before the system returns to normal refrigeration operation.

Question 111: What happens to the refrigerant in the condenser?

It expands and drops in pressure
It absorbs heat and evaporates
It is compressed to a higher pressure
It rejects heat and changes from a high-pressure superheated gas to a high-pressure liquid (Correct answer)

Correct answer: It rejects heat and changes from a high-pressure superheated gas to a high-pressure liquid

In the condenser, high-pressure superheated refrigerant gas from the compressor rejects heat to the surrounding medium (air or water). As it loses heat, it desuperheats, condenses from gas to liquid, and may subcool further. This heat rejection is what removes the heat absorbed by the evaporator plus the heat of compression.

Question 112: A refrigeration system shows high discharge pressure, high suction pressure, and low superheat. What is the most likely cause?

Faulty compressor discharge valves
Restricted liquid line filter-drier
Refrigerant overcharge (Correct answer)
Refrigerant undercharge

Correct answer: Refrigerant overcharge

High discharge pressure, high suction pressure, and low superheat together indicate refrigerant overcharge — excess refrigerant floods the evaporator (low superheat) and overwhelms the condenser (high discharge pressure).

Question 113: After repairing a refrigerant system leak, what two steps are mandatory before recharging with refrigerant?

Pressure test with refrigerant, then add a drier and recharge
Perform a leak test, then evacuate the system to deep vacuum (Correct answer)
Run the compressor briefly on nitrogen, then recharge to nameplate weight
Flush the system with dry nitrogen, then recharge immediately

Correct answer: Perform a leak test, then evacuate the system to deep vacuum

A post-repair leak test confirms the repair is sound, and a deep vacuum evacuation removes air and moisture before refrigerant is introduced to prevent acid formation and system damage.

Question 114: What does a thermal overload relay do in a motor starter circuit?

It measures motor winding temperature directly and shuts down on overtemperature
It senses motor current and opens the control circuit if sustained overcurrent is detected, protecting the motor from overheating due to overload (Correct answer)
It reverses motor rotation if the motor starts in the wrong direction
It provides power factor correction for the motor

Correct answer: It senses motor current and opens the control circuit if sustained overcurrent is detected, protecting the motor from overheating due to overload

A thermal overload relay uses a bimetallic element or electronic sensor to monitor motor current; if the motor draws excessive current for a sustained period (indicating mechanical overload or locked rotor), the relay trips and removes the motor from the circuit.

Question 115: In an HVAC electrical schematic, what does a normally open (NO) contact symbol indicate?

A contact that is always electrically connected and cannot be opened
A contact that opens automatically on power failure for safety
A contact used exclusively in three-phase circuits
A contact that is open (non-conducting) in its de-energized (resting) state and closes when the associated coil or mechanism is actuated (Correct answer)

Correct answer: A contact that is open (non-conducting) in its de-energized (resting) state and closes when the associated coil or mechanism is actuated

A normally open contact is open (circuit broken) when the relay or switch is in its rest state, and closes (conducts) when the coil is energized or the switch is actuated, completing the circuit.

Question 116: What is the difference between a start capacitor and a run capacitor?

They are identical and interchangeable
A start capacitor is larger; a run capacitor is smaller
Start capacitors are used only in heating; run capacitors only in cooling
A start capacitor provides high torque during motor startup and disconnects via a relay; a run capacitor stays in the circuit continuously to improve efficiency (Correct answer)

Correct answer: A start capacitor provides high torque during motor startup and disconnects via a relay; a run capacitor stays in the circuit continuously to improve efficiency

A start capacitor provides a large capacitance boost (typically 100-400 µF) for high starting torque and is disconnected by a potential relay or current relay within seconds of starting. A run capacitor provides lower capacitance (typically 5-45 µF) and remains in the circuit during operation to maintain motor efficiency and power factor.

Question 117: How does a cooling tower work with a water-cooled condenser?

The cooling tower cools the condenser water through evaporation of a portion of the water, then returns the cooled water to the condenser (Correct answer)
The cooling tower filters contaminants from the water
The cooling tower stores water for emergency use
The cooling tower heats the water before it enters the condenser

Correct answer: The cooling tower cools the condenser water through evaporation of a portion of the water, then returns the cooled water to the condenser

A cooling tower cools condenser water by spraying it over fill media while ambient air is drawn through. A small portion of the water evaporates, absorbing heat from the remaining water (evaporative cooling). The cooled water collects in the basin and is pumped back to the condenser. This allows water-cooled systems to reject heat very efficiently.

Question 118: What causes compressor short cycling and what are its effects?

Operating at half speed; causes low noise
Running only during peak demand; causes energy savings
Rapidly turning on and off due to low charge, thermostat issues, or high head pressure; causes increased wear, overheating, and premature failure (Correct answer)
Running continuously; causes high efficiency

Correct answer: Rapidly turning on and off due to low charge, thermostat issues, or high head pressure; causes increased wear, overheating, and premature failure

Short cycling is rapid, repeated starting and stopping caused by issues such as low refrigerant charge, faulty thermostat, oversized equipment, high head pressure, or electrical problems. It causes excessive heat buildup in the motor windings, increased mechanical wear on starting components, and significantly reduced compressor life.

Question 119: What is a capillary tube expansion device and what type of system is it most suited for?

A variable-flow tube that adjusts automatically to load changes; suited for large commercial chillers
A tube used to equalize pressure during the off-cycle in heat pumps; not used for expansion
A tube that measures refrigerant quality; suited for diagnostic use only
A fixed-length, small-bore tube that creates a fixed pressure drop by restriction; suited for small, factory-charged systems with stable loads (Correct answer)

Correct answer: A fixed-length, small-bore tube that creates a fixed pressure drop by restriction; suited for small, factory-charged systems with stable loads

A capillary tube is a simple, fixed-restriction expansion device that meters refrigerant flow by its length and diameter; it is used in small, sealed systems like household refrigerators and window air conditioners with relatively stable loads.

Question 120: What is latent heat and why is it significant in the refrigeration cycle?

The heat measured by a thermometer
The heat generated by friction in the compressor
The heat stored in the building walls
The heat energy absorbed or released during a phase change (liquid to gas or gas to liquid) without a temperature change (Correct answer)

Correct answer: The heat energy absorbed or released during a phase change (liquid to gas or gas to liquid) without a temperature change

Latent heat is the energy absorbed or released when a substance changes phase without changing temperature. In refrigeration, the large amount of latent heat absorbed during evaporation provides the cooling effect, and the latent heat released during condensation is how the system rejects heat. This is far more effective than sensible heat transfer alone.

Question 121: What Canadian electrical code (CEC) requires HVAC technicians to follow when performing electrical work on refrigeration equipment?

The National Fire Code of Canada
The Canadian Electrical Code (CSA C22.1), adopted by all provinces and territories (Correct answer)
The CSA B52 Mechanical Refrigeration Code
The ASHRAE 15 Safety Standard for Mechanical Refrigeration

Correct answer: The Canadian Electrical Code (CSA C22.1), adopted by all provinces and territories

The Canadian Electrical Code (CEC), published as CSA C22.1, is the primary electrical installation standard adopted by all Canadian provinces and territories and governs all electrical work including HVAC equipment wiring.

Question 122: What is the temperature difference (TD) across an evaporator and what does it indicate?

The difference between indoor and outdoor temperatures
The difference between the air temperature entering the evaporator and the refrigerant saturation temperature; it indicates proper coil sizing and airflow (Correct answer)
The difference between refrigerant discharge and suction temperatures
The temperature change of the refrigerant through the compressor

Correct answer: The difference between the air temperature entering the evaporator and the refrigerant saturation temperature; it indicates proper coil sizing and airflow

Evaporator TD is the difference between the entering air temperature and the refrigerant saturation (boiling) temperature inside the coil. A typical TD for comfort cooling is 10°C to 12°C (18°F to 22°F). A higher TD indicates restricted airflow, dirty coils, or an undersized coil; a lower TD may indicate an oversized coil or excess refrigerant.

Question 123: What is the function of a high-pressure safety control (high-pressure cutout) in a refrigeration system?

To shut down the compressor if discharge pressure exceeds a safe limit, preventing equipment damage and refrigerant venting (Correct answer)
To limit the maximum current draw of the compressor motor
To signal a low refrigerant charge condition to the building management system
To prevent the condenser fan from operating when ambient temperature is too high

Correct answer: To shut down the compressor if discharge pressure exceeds a safe limit, preventing equipment damage and refrigerant venting

A high-pressure cutout is a safety switch that opens the compressor control circuit when discharge pressure rises above the set point, protecting the system from excessive pressure that could damage components or cause refrigerant leaks.

Question 124: When evacuating a refrigeration system before charging, what vacuum level is considered acceptable under industry best practices in Canada?

A vacuum equivalent to 15 psi below atmospheric pressure
10,000 microns, which is sufficient to remove moisture
Any reading below 29 inches Hg on a manifold gauge
500 microns (500 µm Hg) or lower, verified by a micron gauge with the vacuum pump isolated (Correct answer)

Correct answer: 500 microns (500 µm Hg) or lower, verified by a micron gauge with the vacuum pump isolated

Industry best practice and many manufacturers require the system to reach 500 microns (µm Hg) or lower, confirmed with a micron gauge after the vacuum pump is isolated, to ensure adequate moisture and non-condensable removal before charging.

Question 125: What is the purpose of the common terminal (C) on a 24V HVAC thermostat wiring connection?

To connect the thermostat to the building automation system network
To provide the return (neutral) path for the 24V control circuit, completing the circuit back to the transformer (Correct answer)
To signal the outdoor unit to energize the reversing valve
To provide a switched 24V signal to the cooling circuit

Correct answer: To provide the return (neutral) path for the 24V control circuit, completing the circuit back to the transformer

The C terminal (common) provides the return path for 24V AC current back to the transformer secondary, completing the control circuit; without it, smart thermostats and WiFi thermostats cannot draw the power they need.

Question 126: What does a dual-pressure control combine into a single device?

A pressure transducer and a flow switch for pump protection
A temperature controller and a pressure controller for simultaneous monitoring
A low-pressure cutout and a differential pressure switch for filter monitoring
A high-pressure cutout and a low-pressure cutout in one housing, with separate adjustable setpoints for each (Correct answer)

Correct answer: A high-pressure cutout and a low-pressure cutout in one housing, with separate adjustable setpoints for each

A dual-pressure control combines a high-pressure safety cutout and a low-pressure cutout (or low-pressure pump-down control) in one device, allowing both functions with a single installation.

Red Seal Refrigeration and Air Conditioning Mechanic (313A)

The Red Seal 313A interprovincial exam certifies Refrigeration and Air Conditioning Mechanics across Canada, testing knowledge of HVAC/R system planning, installation, commissioning, maintenance, and service in residential, commercial, and industrial settings.

125

Questions

240 min

Time Limit

70%

To Pass

Checking for saved progress...

Exam Rules

You can skip questions and return to them later
Flag questions for review before submitting
No feedback shown until you submit the entire exam
Unanswered questions count as wrong — answer everything
10 pretest questions are mixed in and don't affect your score
Timer auto-submits when time runs out
Your progress is auto-saved every 30 seconds

These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

Sources & references

Exam facts on this page (fees, format, dates, passing scores) are checked against these official sources; the date is our last check. Editorial policy

skilledtradesontario.ca — Score validity, eligibility, retake policy, renewal, fees, test delivery, passing score, score release, time limit · verified Oct 2026
red-seal.ca — Exam format · verified Oct 2026