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

Question 1: In an HVAC electrical schematic, what does a normally open (NO) contact symbol indicate?

A contact that opens automatically on power failure for safety
A contact that is always electrically connected and cannot be opened
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)
A contact used exclusively in three-phase circuits

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

To convert single-phase power to three-phase power for 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 measure and display voltage and current to the compressor
To protect against ground faults in the power supply

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

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

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

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

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 5: In a semi-hermetic compressor, what maintenance advantage does it offer over a fully hermetic compressor?

It can be disassembled and repaired in the field, allowing valve replacement and motor rewinding (Correct answer)
It does not require a crankcase heater because the shell is always warm
It operates at lower noise levels than fully hermetic compressors
It never requires oil changes because it uses synthetic refrigerant oil

Correct answer: It can be disassembled and repaired in the field, allowing valve replacement and motor rewinding

Semi-hermetic compressors have bolted access covers that allow the technician to access and replace valves, pistons, connecting rods, and even rewind the motor, extending the useful life of the compressor.

Question 6: What is the purpose of a crankcase heater on a refrigeration compressor?

To maintain minimum ambient temperature around the compressor
To heat the discharge gas before it enters the condenser
To keep the oil warm for easier starting in cold weather and to prevent refrigerant migration into the crankcase oil (Correct answer)
To prevent ice formation on the compressor body in low-temperature applications

Correct answer: To keep the oil warm for easier starting in cold weather and to prevent refrigerant migration into the crankcase oil

A crankcase heater prevents refrigerant from migrating and condensing in the compressor oil during off-cycles, which would cause foaming and oil dilution on startup, potentially leading to bearing failure.

Question 7: What is the purpose of the reversing valve in a heat pump system?

To switch the electrical polarity of the compressor motor for reverse operation
To reverse the direction of compressor rotation for heating and cooling modes
To reverse the direction of airflow through the air handler between seasons
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)

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

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 is used only for single-phase motors; delta is only for three-phase motors
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 9: What is a hot gas defrost system?

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

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

Air-cooled condenser
Evaporative condenser
Water-cooled condenser (shell-and-tube or plate heat exchanger) (Correct answer)
Desuperheating 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 11: What is the saturation temperature of a refrigerant?

The temperature at which the refrigerant changes state (boils or condenses) at a given pressure (Correct answer)
The maximum operating temperature of the system
The ambient air temperature at the outdoor unit
The temperature at which the oil separates from the refrigerant

Correct answer: The temperature at which the refrigerant changes state (boils or condenses) at a given pressure

Saturation temperature is the temperature at which a refrigerant changes between liquid and vapour states at a specific pressure. At saturation, liquid and vapour coexist. Every refrigerant has a unique pressure-temperature relationship that technicians use for system diagnosis.

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

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

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 primary function of a metering device in a refrigeration system?

To regulate the speed of the compressor
To measure the amount of refrigerant in the system
To reduce the pressure and temperature of the liquid refrigerant before it enters the evaporator, and to control refrigerant flow rate (Correct answer)
To measure the superheat at the compressor

Correct answer: To reduce the pressure and temperature of the liquid refrigerant before it enters the evaporator, and to control refrigerant flow rate

The metering device (expansion device) serves two critical functions: it reduces the high-pressure liquid refrigerant to a low-pressure mixture of liquid and vapour, and it controls the flow rate of refrigerant into the evaporator to match the system's cooling demand.

Question 14: What is the main advantage of a scroll compressor over a reciprocating compressor?

Lower initial purchase cost
Higher compression ratios suitable for industrial refrigeration
Ability to handle liquid slugging without damage
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 15: What does GWP (Global Warming Potential) measure for refrigerants?

The operating pressure range of the refrigerant
The toxicity level of the refrigerant
The refrigerant's ability to absorb heat in the evaporator
The relative contribution of the refrigerant to greenhouse warming compared to CO2 over 100 years (Correct answer)

Correct answer: The relative contribution of the refrigerant to greenhouse warming compared to CO2 over 100 years

GWP is an index that compares a refrigerant's contribution to climate change relative to carbon dioxide (CO2=1) over a 100-year time horizon.

Question 16: 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 transferred only by radiation
Heat stored in the refrigerant's pressure

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

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)
They use different refrigerants
A fin-and-tube is for heating only; a plate is for cooling only
There is no significant difference

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

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

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

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

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 20: What is the primary function of the evaporator in a refrigeration system?

To condense refrigerant vapour back into liquid
To compress refrigerant vapour to high pressure
To separate oil from the refrigerant vapour
To absorb heat from the refrigerated space or process fluid by evaporating the refrigerant (Correct answer)

Correct answer: To absorb heat from the refrigerated space or process fluid by evaporating the refrigerant

The evaporator absorbs heat from the space or product being cooled as the liquid refrigerant boils and vaporizes at low pressure, providing the refrigeration effect.

Question 21: What is the primary environmental concern with R-410A that is driving its phase-down under the Kigali Amendment?

High toxicity to HVAC technicians
Extreme flammability risk
Very high global warming potential (GWP ~2088) (Correct answer)
High ozone depletion potential

Correct answer: Very high global warming potential (GWP ~2088)

R-410A has a GWP of approximately 2088, making it a potent greenhouse gas; the Kigali Amendment to the Montreal Protocol requires the phase-down of high-GWP HFCs including R-410A.

Question 22: What is a current sensing relay and where is it used?

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

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

Rotary, centrifugal, and axial
Open (external drive), semi-hermetic (serviceable), and hermetic (welded/sealed) (Correct answer)
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 24: What is the coefficient of performance (COP) in a refrigeration system?

The percentage of refrigerant that evaporates
The number of refrigeration cycles per hour
The speed at which the compressor operates
The ratio of cooling capacity (heat removed) to the energy input (work done by compressor) (Correct answer)

Correct answer: The ratio of cooling capacity (heat removed) to the energy input (work done by compressor)

COP is the ratio of useful cooling output to the work input required to achieve it. A COP of 3 means the system removes 3 units of heat for every 1 unit of electrical energy consumed. Higher COP indicates greater efficiency. COP varies with operating conditions, particularly evaporator and condenser temperatures.

Question 25: 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?

A failed TXV stuck in the open position
Dirty condenser coil blocking heat rejection
Failed compressor discharge or suction valves, causing the compressor to pump poorly (Correct answer)
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 26: What is the primary function of compressor oil in a refrigeration system?

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

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

Refrigerant overcharge (Correct answer)
Faulty compressor discharge valves
Restricted liquid line filter-drier
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 28: What is the purpose of the oil separator in a refrigeration system?

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

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 29: 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 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)
To modulate liquid refrigerant flow continuously based on cooling demand

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 30: What is the split between sensible and latent cooling in an evaporator?

The split only matters in commercial systems
Sensible is for heating; latent is for cooling
Sensible cooling changes temperature; latent cooling removes moisture — the ratio affects both comfort and coil selection (Correct answer)
There is only sensible cooling in an evaporator

Correct answer: Sensible cooling changes temperature; latent cooling removes moisture — the ratio affects both comfort and coil selection

Evaporators perform both sensible cooling (lowering air temperature) and latent cooling (removing moisture by condensing it on the coil). The sensible heat ratio (SHR) describes the proportion of each. In humid climates, more latent capacity is needed; in dry climates, mostly sensible cooling is required. Coil selection and airflow affect this ratio.

Question 31: What is the primary purpose of the refrigeration cycle in an HVAC system?

To generate heat through combustion
To transfer heat from a low-temperature region to a high-temperature region (Correct answer)
To increase the pressure of ambient air
To convert mechanical energy into electrical energy

Correct answer: To transfer heat from a low-temperature region to a high-temperature region

The refrigeration cycle transfers heat from a cool space to a warmer environment by using a refrigerant that absorbs and releases heat as it changes phase.

Question 32: What does a phase-loss relay protect against in a three-phase compressor installation?

Detecting the loss of one phase of the three-phase supply, which would cause the motor to overheat and potentially burn out (Correct answer)
Protecting the compressor from reverse rotation due to miswired phases
Preventing the compressor from starting when the power supply frequency is out of range
Protecting against voltage spikes from lightning or utility switching

Correct answer: Detecting the loss of one phase of the three-phase supply, which would cause the motor to overheat and potentially burn out

A phase-loss relay monitors all three phases of the power supply; if one phase is lost, the motor attempts to run on two phases (single phasing), drawing excessive current and overheating, so the relay shuts it down immediately.

Question 33: What is the purpose of a suction line filter-drier?

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

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

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)
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 variable-flow tube that adjusts automatically to load changes; suited for large commercial chillers

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 35: What is subcooling in a refrigeration system?

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

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

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

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 37: What is the purpose of non-condensable gas purging in a refrigeration system?

To purge oil accumulation from the condenser
To blow out debris from the condenser coil fins
To eliminate air or nitrogen trapped in the system that raises condensing pressure and reduces efficiency (Correct answer)
To remove excess refrigerant charge from the high side

Correct answer: To eliminate air or nitrogen trapped in the system that raises condensing pressure and reduces efficiency

Non-condensable gases such as air or nitrogen do not condense and accumulate at the top of the condenser, artificially raising discharge pressure and reducing heat transfer efficiency.

Question 38: What is the purpose of a high-pressure safety switch (cutout) on a refrigeration system?

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

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

The critical point only
The two-phase (liquid-vapour) mixture region (Correct answer)
The superheated vapour region
The subcooled liquid 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 40: What is the function of a high-pressure safety control (high-pressure cutout) in a refrigeration system?

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

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 41: 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)
Standard paste solder flux is sufficient
No flux is needed on any copper joint
Flux is only required when using oxygen-acetylene equipment

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 42: What does a high suction pressure reading typically indicate in a refrigeration system?

Compressor valve failure causing low compression
High heat load or overcharge of refrigerant (Correct answer)
Refrigerant undercharge
Blocked liquid line filter-drier

Correct answer: High heat load or overcharge of refrigerant

High suction pressure usually indicates an excessive heat load on the evaporator or a refrigerant overcharge, both of which cause more refrigerant vapour to enter the compressor suction.

Question 43: What does a dual-pressure control combine into a single device?

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)
A pressure transducer and a flow switch for pump protection

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.

Question 44: 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 is optional if the system is new
Evacuation removes excess refrigerant; target is 0 psig
Evacuation removes oil; target is atmospheric pressure

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 45: What is a triple evacuation and when is it recommended?

Evacuating the high side, low side, and oil sump separately
Three cycles of pulling a vacuum then breaking with dry nitrogen, followed by a final deep vacuum; recommended for systems with significant moisture contamination (Correct answer)
Three different vacuum pumps used simultaneously
Evacuating the system three times in a row

Correct answer: Three cycles of pulling a vacuum then breaking with dry nitrogen, followed by a final deep vacuum; recommended for systems with significant moisture contamination

A triple evacuation involves: (1) pulling a vacuum, (2) breaking the vacuum with dry nitrogen to atmospheric pressure, (3) repeating the vacuum and nitrogen break, and (4) pulling a final deep vacuum to 500 microns or below. The nitrogen sweeps help remove moisture more effectively than a single deep vacuum alone.

Question 46: In the vapour-compression refrigeration cycle, at which component does the refrigerant absorb heat from the space being cooled?

Expansion valve
Evaporator (Correct answer)
Condenser
Compressor

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 47: 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 energy absorbed or released during a phase change (liquid to gas or gas to liquid) without a temperature change (Correct answer)
The heat stored in the building walls

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 48: 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 heats the water before it enters the condenser
The cooling tower stores water for emergency use

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 49: What is a defrost timer and how does it function in a heat pump system?

A timer that shuts the system off after a set period
A timer that controls the indoor fan speed
A timer that schedules maintenance reminders
A control that initiates and terminates defrost cycles at set intervals or based on demand, reversing the system to melt frost accumulated on the outdoor coil (Correct answer)

Correct answer: A control that initiates and terminates defrost cycles at set intervals or based on demand, reversing the system to melt frost accumulated on the outdoor coil

A defrost control (timer-based or demand-based) manages the defrost cycle when frost accumulates on the outdoor coil during heating mode. Time-initiated defrost runs at set intervals (e.g., every 90 minutes). Demand defrost uses sensors (temperature differential, air pressure) to initiate defrost only when needed, improving efficiency.

Question 50: What is the purpose of a crankcase pressure regulator (CPR) valve?

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

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 51: UV dye leak detection requires which additional piece of equipment to be effective?

A UV (black light) lamp and UV-filtering safety glasses (Correct answer)
An infrared thermal camera
A refrigerant identifier to confirm dye compatibility
A digital manifold gauge set to confirm suction side leaks

Correct answer: A UV (black light) lamp and UV-filtering safety glasses

UV fluorescent dye only becomes visible when illuminated by an ultraviolet (black light) lamp, and UV-filtering glasses enhance contrast to reveal even faint traces of dye.

Question 52: What is a transformer in an HVAC control circuit and what voltage does it typically provide?

It converts 24V to 240V for the compressor
It converts AC to DC for electronic controls
It steps down line voltage (240V or 120V) to 24V AC to power the thermostat and control circuit safely (Correct answer)
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 53: Under Canadian federal refrigerant regulations, technicians must repair leaks in systems with a refrigerant charge above what threshold within 30 days of detection?

Any system regardless of charge size
Only R-22 and other HCFC systems
Systems with a charge above 3 kg (Correct answer)
Systems with a charge above 100 kg

Correct answer: Systems with a charge above 3 kg

Under Canada's Ozone-depleting Substances and Halocarbon Alternatives Regulations (CEPA), systems containing more than 3 kg of refrigerant must have detected leaks repaired within 30 days.

Question 54: What is the temperature difference (TD) across an evaporator and what does it indicate?

The difference between refrigerant discharge and suction temperatures
The temperature change of the refrigerant through the compressor
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 indoor and outdoor temperatures

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 55: What indicates a faulty compressor valve in a reciprocating compressor?

Low discharge pressure, high suction pressure, reduced capacity, and higher than normal compressor amperage (Correct answer)
Frost on the liquid line
Normal operating pressures and temperatures
Excessively low amperage

Correct answer: Low discharge pressure, high suction pressure, reduced capacity, and higher than normal compressor amperage

A leaking compressor valve allows gas to bypass between the high and low sides. This results in: lower than normal discharge (head) pressure, higher than normal suction pressure, reduced cooling/heating capacity, and higher amperage as the compressor works harder to maintain pressure differential.

Question 56: What is the purpose of a defrost timer in a refrigeration system?

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

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 57: 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 measure refrigerant charge by weight
To store liquid refrigerant and ensure a steady supply to the expansion device (Correct answer)

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

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)
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

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

Refrigerant recovery only
Internal service including valve plate inspection/replacement, bearing inspection, motor winding checks, and oil analysis (Correct answer)
Electrical terminal tightening 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 60: When brazing copper-to-copper refrigerant joints, which brazing alloy is most commonly specified?

BCuP-5 (15% silver, copper-phosphorus) (Correct answer)
Soft solder (50/50 tin-lead)
BCuP-2 (copper-phosphorus, no silver)
BAg-7 (56% 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 61: What is the purpose of a distributor nozzle installed at the inlet of a multi-circuit evaporator?

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

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 62: What safety precautions must be taken when handling refrigerants?

No special precautions are needed
Only wear a hard hat
Work in well-ventilated areas, wear safety glasses and gloves, use proper recovery equipment, never heat cylinders with open flame, and have a refrigerant leak detector available (Correct answer)
Only work outdoors

Correct answer: Work in well-ventilated areas, wear safety glasses and gloves, use proper recovery equipment, never heat cylinders with open flame, and have a refrigerant leak detector available

Refrigerant safety precautions include: work in well-ventilated areas (refrigerants displace oxygen and some decompose into toxic gases near flames), wear safety glasses (liquid refrigerant causes frostbite on contact), wear gloves, never use open flames to heat cylinders, monitor for leaks with proper detectors, and know the SDS for each refrigerant.

Question 63: Why must dry nitrogen be purged through copper tubing during the brazing process?

To cool the tubing faster after brazing
To pressure-test the joint immediately after brazing
To prevent cupric oxide scale from forming inside the pipe (Correct answer)
To increase the flow rate of the brazing alloy

Correct answer: To prevent cupric oxide scale from forming inside the pipe

Flowing dry nitrogen displaces oxygen inside the pipe, preventing the formation of copper oxide scale that can contaminate compressor valves and metering devices.

Question 64: What is the difference between refrigerant recovery, recycling, and reclamation?

Recovery is for CFC only; recycling is for HFC only
They are all the same process
Recovery removes refrigerant from a system; recycling cleans it for reuse in the field; reclamation reprocesses it to meet new-product specifications at an approved facility (Correct answer)
They differ only in the equipment used

Correct answer: Recovery removes refrigerant from a system; recycling cleans it for reuse in the field; reclamation reprocesses it to meet new-product specifications at an approved facility

Recovery is the process of removing refrigerant from a system into an approved container. Recycling involves field-cleaning recovered refrigerant (removing oil, moisture, and non-condensables) for reuse. Reclamation is factory reprocessing to ARI 700 (new-product) specifications, involving chemical analysis, distillation, and certification.

Question 65: 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
Notification to the building owner at least 24 hours in advance
A brief visual inspection of the space from the entrance
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 66: 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
They refer to the same type of reset
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)

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 67: What does enthalpy represent in refrigeration thermodynamics?

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

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

A valve that opens and closes based on time
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 controls water flow through the condenser
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 69: What is a thermostat and how does a programmable thermostat save energy?

A switch that only turns on heating
A safety device that prevents overheating
A device that measures humidity only
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)

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

A compressor using rotating vanes; advantage is high capacity
A compressor using centrifugal force; advantage is very high capacity
A compressor using a piston and cylinder; advantage is simplicity
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 71: Which TSSA (Technical Standards and Safety Authority) designation is relevant for refrigeration and air conditioning mechanics in Ontario?

Gas Technician (G1/G2/G3)
Pressure Welder
Refrigeration Operating Engineer (Correct answer)
Fuel Oil Technician

Correct answer: Refrigeration Operating Engineer

TSSA regulates Refrigeration Operating Engineers in Ontario for stationary refrigeration plants, separate from the Red Seal 313A trade qualification which covers installation and service technicians.

Question 72: What is a potential relay and what does it do in a compressor motor circuit?

A relay that controls the reversing valve
A relay that switches between heating and cooling modes
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)
A relay that detects power outages

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 73: What is subcooling in the refrigeration cycle?

Cooling the evaporator below 0°C
The temperature of the liquid refrigerant below its condensing (saturation) temperature at condenser pressure (Correct answer)
Reducing the refrigerant charge below recommended levels
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 74: What is an accumulator and where is it installed in a refrigeration system?

A vessel installed in the liquid line to store excess refrigerant charge
A filter installed at the compressor discharge to remove oil
A vessel installed in the suction line between the evaporator and compressor to catch liquid refrigerant and prevent slugging (Correct answer)
A high-pressure vessel that stores refrigerant during pumpdown

Correct answer: A vessel installed in the suction line between the evaporator and compressor to catch liquid refrigerant and prevent slugging

A suction line accumulator is a vessel that catches any liquid refrigerant or oil carryover from the evaporator, allowing only vapour to enter the compressor suction and protecting against liquid slugging.

Question 75: Where should the sensing bulb of a TXV be mounted?

On the discharge line of the compressor
On the liquid line leaving the condenser
On the suction line at the evaporator outlet, at the 10 o'clock or 2 o'clock position on a horizontal line (Correct answer)
Inside the evaporator coil

Correct answer: On the suction line at the evaporator outlet, at the 10 o'clock or 2 o'clock position on a horizontal line

The TXV sensing bulb must be clamped securely to the suction line at the evaporator outlet. It should be mounted at the 10 o'clock or 2 o'clock position (not on top or bottom) on horizontal lines to avoid oil influence. It must have good thermal contact, be insulated from ambient air, and be located before any external equalizer connection.

Question 76: What is the purpose of a relief valve on a refrigeration pressure vessel under CSA B52?

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)
To balance pressure between the high and low sides of the system during shutdown
To release refrigerant to the atmosphere to reduce system charge during overcharge conditions

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 77: What does megohm testing (megging) a compressor motor winding indicate?

The resistance of the motor windings between terminals to check for open or shorted windings
The capacitance of the motor run capacitor
The insulation resistance of the motor windings to ground, indicating whether insulation breakdown or moisture contamination has occurred (Correct answer)
The inductance of the motor windings to verify correct winding configuration

Correct answer: The insulation resistance of the motor windings to ground, indicating whether insulation breakdown or moisture contamination has occurred

A megohmmeter applies a high DC voltage (typically 500 V) to the motor winding and measures the resistance to ground; low megohm readings indicate degraded insulation, moisture ingress, or early winding failure.

Question 78: 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 79: 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?

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

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

Different refrigerants naturally separate and cause no issues
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)
Mixing is recommended for better performance

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 81: What is superheat in a refrigeration system?

The temperature of refrigerant above its boiling point in the vapour state (Correct answer)
The heat added by the compressor motor
The temperature difference across the condenser
The excess pressure above design operating pressure

Correct answer: The temperature of refrigerant above its boiling point in the vapour state

Superheat is the number of degrees the refrigerant vapour is above its saturation (boiling) temperature at a given pressure, measured at the evaporator outlet or compressor suction.

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

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

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

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

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

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)
A start capacitor is larger; a run capacitor is smaller
They are identical and interchangeable

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 86: In a heat pump system, how does the cycle differ from a standard air conditioning cycle?

A reversing valve changes the direction of refrigerant flow, allowing the system to heat or cool by swapping the functions of the indoor and outdoor coils (Correct answer)
Heat pumps use a different refrigerant
There is no difference between them
Heat pumps operate at higher pressures

Correct answer: A reversing valve changes the direction of refrigerant flow, allowing the system to heat or cool by swapping the functions of the indoor and outdoor coils

A heat pump uses a reversing valve (four-way valve) to reverse the direction of refrigerant flow. In cooling mode, the outdoor coil is the condenser and the indoor coil is the evaporator. In heating mode, the functions are reversed — the outdoor coil absorbs heat (evaporator) and the indoor coil rejects heat (condenser).

Question 87: What happens to system performance if a TXV sensing bulb loses its charge?

The valve closes because the opening force is lost, starving the evaporator of refrigerant and causing low suction pressure and poor cooling (Correct answer)
Only the defrost cycle is affected
The valve opens fully, flooding the compressor
The system operates normally

Correct answer: The valve closes because the opening force is lost, starving the evaporator of refrigerant and causing low suction pressure and poor cooling

If the TXV sensing bulb loses its refrigerant charge (from a leak or physical damage), the opening force is lost. The spring and equalizer forces push the valve closed, severely restricting or stopping refrigerant flow to the evaporator. This results in a starved evaporator, very low suction pressure, high superheat, and little to no cooling.

Question 88: What is the unit of heat energy used in Canadian HVAC calculations?

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

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 89: What is a capillary tube and in what applications is it commonly used?

A tube used to connect pressure gauges
A small-diameter fixed-restriction tube that meters refrigerant by friction; commonly used in residential refrigerators, window air conditioners, and small heat pumps (Correct answer)
A tube that measures capillary pressure in the system
A large-diameter pipe for refrigerant storage

Correct answer: A small-diameter fixed-restriction tube that meters refrigerant by friction; commonly used in residential refrigerators, window air conditioners, and small heat pumps

A capillary tube is a long, small-diameter (0.5 mm to 2 mm) copper tube that meters refrigerant through friction-based pressure drop. It is a fixed restriction with no moving parts, making it inexpensive and reliable. It is used in small, fixed-capacity systems where the load is relatively constant.

Question 90: What is 'liquid slugging' in a compressor and why is it dangerous?

Liquid refrigerant entering the compressor cylinders, which can cause mechanical damage due to incompressibility of liquids (Correct answer)
A buildup of sludge on compressor valves reducing efficiency
Excessive oil circulation through the system causing liquid hammer in pipes
Oil foaming in the crankcase that starves bearings of lubrication

Correct answer: Liquid refrigerant entering the compressor cylinders, which can cause mechanical damage due to incompressibility of liquids

Liquid slugging occurs when liquid refrigerant enters the compressor, and because liquids cannot be compressed, the compressor valves and pistons can be severely damaged or destroyed.

Question 91: What is the purpose of a run capacitor on a compressor motor?

To start the motor spinning
To regulate voltage to the motor
To improve the efficiency and power factor of the motor by creating a phase shift in the run winding during normal operation (Correct answer)
To store backup power for outages

Correct answer: To improve the efficiency and power factor of the motor by creating a phase shift in the run winding during normal operation

A run capacitor remains in the circuit during normal motor operation. It creates a phase shift between the start and run windings, improving motor efficiency, power factor, and torque. A failed run capacitor causes the motor to run inefficiently, draw higher amperage, overheat, and eventually fail.

Question 92: What damage can liquid slugging cause to a reciprocating compressor?

It causes the motor to overheat
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

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

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

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

0.034 (Correct answer)
0.05
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 95: How does a balanced-port TXV differ from a standard TXV?

It uses a balanced piston design that eliminates the effect of changing head pressure on valve operation, providing more stable control (Correct answer)
It has two sensing bulbs
It is only used in automotive systems
It uses electronic controls instead of a sensing bulb

Correct answer: It uses a balanced piston design that eliminates the effect of changing head pressure on valve operation, providing more stable control

A balanced-port TXV uses a dual-ported piston design that neutralizes the effect of inlet (head) pressure on the valve's operation. In a standard TXV, changing head pressure affects the closing force on the valve. The balanced design maintains consistent superheat control regardless of head pressure variations, improving performance in fluctuating ambient conditions.

Question 96: What is the purpose of a time-delay relay (anti-short-cycle timer) in a compressor control circuit?

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

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 97: What is the purpose of an oil trap (inverted P-trap) installed at the base of a vertical refrigerant suction riser?

To prevent liquid refrigerant from entering the compressor during start-up
To collect oil that drains down during the off-cycle and return it to the compressor (Correct answer)
To act as a flow indicator for suction gas velocity
To reduce suction line pressure drop across the riser

Correct answer: To collect oil that drains down during the off-cycle and return it to the compressor

During the off-cycle, oil drains to the lowest point of the riser; the oil trap collects it and re-entrains it in the suction gas flow so it is carried back to the compressor when the system restarts.

Question 98: 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 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)
To record service work completed on a tag attached to the equipment

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 99: What low-GWP refrigerant is being widely adopted as a replacement for R-410A in residential HVAC systems?

R-404A
R-507A
R-123
R-32 (Correct answer)

Correct answer: R-32

R-32 (difluoromethane) has a GWP of 675 — significantly lower than R-410A — and is being widely adopted as a more climate-friendly replacement for residential air conditioning globally, including in Canada.

Question 100: What are the four main components of a basic vapour-compression refrigeration cycle?

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

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

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

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

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)
An evaporator with excessive frost buildup
An evaporator damaged by water flooding

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 103: What is the role of the unloader on a compressor?

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

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 104: 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 warm the refrigerant for faster startup
To preheat the supply air

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

Pressurizing the system with refrigerant to operating pressure to check for leaks
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)
Testing the relief valve by manually lifting it at operating pressure
Measuring suction and discharge pressures with a manifold gauge after startup

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 106: What does the CSA B52 Mechanical Refrigeration Code govern in Canada?

The performance testing of residential air conditioners for ENERGY STAR rating
The certification requirements for refrigeration technicians
The transportation of refrigerant cylinders by road and rail
The design, construction, installation, and testing of refrigeration and air conditioning systems in Canada (Correct answer)

Correct answer: The design, construction, installation, and testing of refrigeration and air conditioning systems in Canada

CSA B52 is the Canadian standard that governs the design, construction, installation, testing, and maintenance of mechanical refrigeration systems, and it is adopted by provincial codes across Canada.

Question 107: What happens to the refrigerant in the condenser?

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

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 108: What happens to the boiling point of a refrigerant as pressure increases?

It increases (Correct answer)
It remains constant
It decreases
It becomes unpredictable

Correct answer: It increases

As pressure increases, the boiling (saturation) temperature of a refrigerant also increases, which is why high-side pressure corresponds to higher condensing temperatures.

Question 109: What is the difference between a flooded evaporator and a dry expansion (DX) evaporator?

A flooded evaporator uses water as a secondary coolant; a DX evaporator uses only refrigerant
A flooded evaporator has a TXV; a DX evaporator has a fixed orifice
A flooded evaporator is always filled with liquid refrigerant; a DX evaporator allows the refrigerant to fully evaporate before the outlet (Correct answer)
A flooded evaporator operates at higher pressure; a DX evaporator operates at lower pressure

Correct answer: A flooded evaporator is always filled with liquid refrigerant; a DX evaporator allows the refrigerant to fully evaporate before the outlet

In a flooded evaporator, the coil is completely filled with boiling liquid refrigerant for maximum heat transfer; in a DX (direct expansion) evaporator, the refrigerant fully evaporates within the coil, exiting as superheated vapour.

Question 110: What type of compressor uses pistons driven by a crankshaft to compress refrigerant?

Reciprocating (piston) compressor (Correct answer)
Scroll compressor
Centrifugal compressor
Screw compressor

Correct answer: Reciprocating (piston) compressor

A reciprocating compressor uses pistons connected to a crankshaft that move up and down in cylinders to compress refrigerant vapour, and is one of the most common types in commercial refrigeration.

Question 111: Why is reaming the inside of copper tubing after cutting with a wheel cutter a mandatory step?

To improve brazing alloy adhesion to the tube wall
To increase the internal bore diameter for higher refrigerant flow
To remove the internal burr that restricts flow and can contaminate the system (Correct answer)
To allow the fitting socket to slide freely over the tube end

Correct answer: To remove the internal burr that restricts flow and can contaminate the system

A wheel cutter leaves a raised internal burr that restricts refrigerant and oil flow, and can break off to contaminate metering devices, compressor valves, and strainers.

Question 112: What symptom would a restricted liquid line filter-drier produce in a refrigeration system?

Oil logging in the evaporator coil
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
High suction pressure and low superheat

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 113: What is the purpose of the compressor in the refrigeration cycle?

To filter impurities from the refrigerant
To raise the pressure and temperature of the refrigerant vapour so it can reject heat in the condenser (Correct answer)
To reduce the pressure of the refrigerant
To cool the refrigerant

Correct answer: To raise the pressure and temperature of the refrigerant vapour so it can reject heat in the condenser

The compressor raises the pressure and temperature of the refrigerant vapour from the evaporator. By increasing the pressure, the condensing temperature rises above the ambient temperature, allowing the condenser to reject heat to the surroundings. The compressor is the component that drives the entire cycle.

Question 114: When recovering refrigerant from a system in Canada, what equipment standard must the recovery machine meet?

CSA B52 Mechanical Refrigeration Code requirements for pressure vessels
TSSA Pressure Equipment Safety Regulations
ULC S10 (Standard for Flammable and Combustible Liquids)
UL 1963 / ARI 740 standard for refrigerant recovery/recycling equipment (Correct answer)

Correct answer: UL 1963 / ARI 740 standard for refrigerant recovery/recycling equipment

Recovery equipment used in Canada must meet UL 1963 / ARI 740 (now AHRI 740) standards, which specify performance requirements for refrigerant recovery and recycling machines.

Question 115: What is the function of a low-pressure safety switch in a refrigeration system?

To start the compressor when pressure builds up
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 maintain minimum suction pressure for efficiency
To control the expansion valve opening

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 116: 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 that uses electrical resistance heating to prevent ice formation on the valve body
A valve that automatically detects the type of refrigerant and adjusts accordingly
A valve with an electronic display for monitoring refrigerant flow rate

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

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

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

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

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 119: Under Canada's Environmental Protection Act, what is the maximum allowable leak rate for commercial refrigeration systems before repairs are required?

There is no regulated limit
50% per year is acceptable
Only total loss requires reporting
Systems containing more than a threshold amount of refrigerant must repair leaks within a specified timeframe, and annual leak rates exceeding approximately 10-20% (depending on province) require mandatory reporting and repair (Correct answer)

Correct answer: Systems containing more than a threshold amount of refrigerant must repair leaks within a specified timeframe, and annual leak rates exceeding approximately 10-20% (depending on province) require mandatory reporting and repair

Canadian federal and provincial regulations require operators of commercial and industrial refrigeration systems to track refrigerant usage, repair identified leaks promptly, and report systems exceeding allowable annual leak rates. Specific thresholds vary by province but generally range from 10% to 20% of total charge. Chronic leaking systems may face fines or mandatory replacement.

Question 120: What is the function of a motor start capacitor in a single-phase PSC or CSIR compressor?

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

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 121: In a standard vapour-compression cycle, which process occurs in the compressor?

Isentropic compression of refrigerant vapour (Correct answer)
Isothermal expansion
Throttling of liquid refrigerant
Isobaric heat rejection

Correct answer: Isentropic compression of refrigerant vapour

The ideal compressor process is isentropic (adiabatic and reversible) compression, raising both the pressure and temperature of the refrigerant vapour.

Question 122: What maintenance should be performed on evaporator coils?

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

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

It converts AC current to DC current for electronic control boards
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)
It steps up voltage from 24V to 120V for control circuit power
It converts three-phase current to single-phase for metering purposes

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

To measure voltage
To convert AC power to DC
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 protect against lightning strikes

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

Presence of moisture in the refrigerant circuit
High refrigerant velocity in the pipe indicating a restriction
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 126: What is the minimum recommended overlap length for a brazed socket joint in refrigerant copper tubing?

Equal to the tube wall thickness
Equal to the tube outside diameter (Correct answer)
Three times the tube wall thickness
Half the tube outside diameter

Correct answer: Equal to the tube outside diameter

The minimum overlap for a brazed socket joint should equal the tube outside diameter to provide adequate joint strength and a leak-free seal.

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%

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