313D Residential Air Conditioning Systems Mechanic — Questions and Answers

Question 1: What is the primary purpose of the subcooling process that occurs in the condenser?

To ensure only vapor enters the compressor.
To absorb maximum heat in the evaporator.
To increase the pressure of the refrigerant vapor.
To prevent flash gas from forming before the metering device. (Correct answer)

Correct answer: To prevent flash gas from forming before the metering device.

Subcooling is the process of cooling the liquid refrigerant below its saturation temperature after it has fully condensed. This ensures that a solid column of liquid refrigerant reaches the metering device, preventing bubbles of vapor (flash gas) from forming prematurely, which would reduce the efficiency of the metering device and the evaporator.

Question 2: What is the primary difference between refrigerant 'recovery,' 'recycling,' and 'reclaiming'?

Recovery=AHRI 700 purity; recycling=on-site cleaning; reclaiming=remove from system
Recovery=remove from system; recycling=oil separation/filter on-site; reclaiming=AHRI 700 purity at certified facility (Correct answer)
They are interchangeable terms with no technical distinction
Recycling and reclaiming are both done at certified facilities; recovery is done on-site

Correct answer: Recovery=remove from system; recycling=oil separation/filter on-site; reclaiming=AHRI 700 purity at certified facility

EPA defines recovery as removing refrigerant from a system, recycling as basic on-site cleaning (oil separation, filtering), and reclaiming as reprocessing to AHRI 700 purity at a certified facility.

Question 3: Under the 2021 International Residential Code, what is the minimum required capacity for a condensate overflow shutoff device?

It must activate within 60 seconds of overflow detection
It must handle twice the rated condensate flow
There is no capacity requirement, only a location requirement
The device must stop the unit before the overflow pan fills (Correct answer)

Correct answer: The device must stop the unit before the overflow pan fills

The IRC requires overflow shutoff devices to stop unit operation before condensate overflows the secondary pan, preventing water damage regardless of specific flow capacity.

Question 4: When using a clamp-on ammeter to measure compressor current, you clamp around only one power conductor. Why?

To measure the current in one leg without cancellation from opposing current flow (Correct answer)
Both conductors must be clamped for accurate readings
Because the other conductor carries 24V control voltage
To avoid damaging the meter at high amperage

Correct answer: To measure the current in one leg without cancellation from opposing current flow

Clamping around both conductors simultaneously causes the opposing magnetic fields to cancel out, resulting in a near-zero reading.

Question 5: On a residential AC system, what is the role of the low-voltage common wire (C-wire) connected to the thermostat?

To ground the thermostat body to the air handler chassis
To complete the 24V circuit by providing a return path to the transformer secondary (Correct answer)
To send the cooling call signal to the contactor
To supply 24V power to the thermostat display

Correct answer: To complete the 24V circuit by providing a return path to the transformer secondary

The C-wire is the common terminal of the 24V transformer secondary, completing the circuit for thermostat operation and smart thermostat power.

Question 6: A technician measures 0.80 inches W.C. total external static pressure on a system rated for 0.50 inches W.C. What corrective action should be taken first?

Add refrigerant to lower head pressure
Replace the air handler with a higher-capacity unit
Inspect the duct system for restrictions, undersized ducts, or dirty filters (Correct answer)
Increase blower speed immediately

Correct answer: Inspect the duct system for restrictions, undersized ducts, or dirty filters

Elevated external static pressure most often results from duct restrictions, undersizing, or a clogged filter rather than a blower or refrigerant issue.

Question 7: A technician measures the total external static pressure (TESP) of a residential air handler and finds it to be 1.1 inches of water column (in. w.c.). The manufacturer's data plate specifies a maximum TESP of 0.5 in. w.c. What is the most likely consequence of this high static pressure reading?

Overamping of the indoor blower motor due to reduced load.
Normal system operation with no adverse effects.
Increased airflow (CFM) and improved system efficiency.
Reduced airflow (CFM) and potential for evaporator coil freezing. (Correct answer)

Correct answer: Reduced airflow (CFM) and potential for evaporator coil freezing.

High total external static pressure indicates excessive resistance in the duct system. This forces the blower motor to work harder to move less air, resulting in reduced CFM. Low airflow across the evaporator coil can cause its temperature to drop below freezing, leading to ice formation.

Question 8: Which duct construction standard is most commonly referenced for residential and light commercial sheet metal ductwork in the United States?

NFPA 90A
SMACNA HVAC Duct Construction Standards (Correct answer)
ACCA Manual D
ASHRAE Standard 62.1

Correct answer: SMACNA HVAC Duct Construction Standards

SMACNA HVAC Duct Construction Standards define material gauges, joint types, and reinforcement for sheet metal ductwork fabrication.

Question 9: A motor nameplate shows FLA = 8A and SF = 1.15. What does the service factor (SF) indicate?

The motor can be operated continuously at 115% of its rated load without damage (Correct answer)
The motor efficiency at full load is 115%
The motor starts at 115% of rated voltage
The motor requires a capacitor rated 15% above the FLA

Correct answer: The motor can be operated continuously at 115% of its rated load without damage

A service factor of 1.15 means the motor can handle 15% above its rated load on a continuous basis without exceeding its thermal limits.

Question 10: After completing a residential system installation and commissioning, which parameter should the technician record on the startup documentation for future reference?

Date of the last refrigerant purchase receipt
Actual measured suction pressure, discharge pressure, superheat, subcooling, and Delta-T at design conditions (Correct answer)
Serial number of the vacuum pump used
Homeowner's preferred thermostat schedule

Correct answer: Actual measured suction pressure, discharge pressure, superheat, subcooling, and Delta-T at design conditions

Recording actual operating pressures, superheat, subcooling, and Delta-T at commissioning establishes a baseline for diagnosing future performance changes.

Question 11: While diagnosing a system with a TXV, a technician measures a consistently high superheat and low suction pressure. The subcooling measured at the condenser outlet is found to be normal to high. Which of the following is the most probable fault?

The condenser coil is dirty and restricted
The TXV sensing bulb has lost its charge (Correct answer)
Inefficient compressor valves
The system is overcharged with refrigerant

Correct answer: The TXV sensing bulb has lost its charge

If the TXV's sensing bulb loses its refrigerant charge, the opening force on the valve's diaphragm is lost. The valve's spring pressure will then overcome the evaporator pressure and force the valve to a nearly closed position. This starves the evaporator of refrigerant, causing low suction pressure and high superheat. The refrigerant that cannot enter the evaporator backs up in the condenser, leading to normal or high subcooling.

Question 12: What does a solid triangle or arrow symbol on a schematic pointing into a wire or component indicate?

A fused disconnect point
Direction of conventional current flow or signal direction (Correct answer)
A mechanical interlock
An adjustable component

Correct answer: Direction of conventional current flow or signal direction

An arrow or triangle on a schematic indicates the direction of conventional current flow or the direction of a signal, helping trace circuit operation.

Question 13: What does SEER stand for and what does it measure?

Standard Equipment Efficiency Rating — maximum BTU capacity
Seasonal Energy Efficiency Ratio — cooling output per unit of electrical energy input over a season (Correct answer)
System Electrical Efficiency Review — compressor amp draw
Seasonal Evaporator Evaporation Rate — pounds of water removed per hour

Correct answer: Seasonal Energy Efficiency Ratio — cooling output per unit of electrical energy input over a season

SEER measures the total cooling output in BTUs divided by the total electrical energy consumed in watt-hours over a typical cooling season.

Question 14: During startup of a new R-410A system, the technician finds subcooling is 25°F and superheat is 4°F. What adjustment is indicated?

Remove refrigerant — system is overcharged (Correct answer)
Add refrigerant — subcooling too low
Increase blower speed to raise superheat
Replace the TXV — it is hunting

Correct answer: Remove refrigerant — system is overcharged

High subcooling (target ~10–15°F) and very low superheat together indicate an overcharged system; refrigerant should be removed.

Question 15: A homeowner complains of short cycling. The technician measures that the compressor runs for less than 2 minutes per cycle. Which component should be tested first?

Condenser coil cleanliness
Capacitor and contactor
High and low pressure safety switches (Correct answer)
Thermostat anticipator or setting

Correct answer: High and low pressure safety switches

Short cycling is frequently caused by pressure switches that trip due to abnormal operating pressures, making them the first item to test.

Question 16: When sizing a thermostat wire for a new residential split system requiring a common (C) wire, what minimum gauge is recommended for runs up to 100 feet?

16 AWG
14 AWG
20 AWG
18 AWG (Correct answer)

Correct answer: 18 AWG

18 AWG thermostat wire is the industry standard minimum for residential control wiring up to 100 feet, providing adequate conductivity for 24V control signals.

Question 17: A technician finds the high-pressure switch tripping repeatedly on a hot day. Condenser coil appears clean. What is the next most likely cause?

Condenser fan motor failure or reduced airflow (Correct answer)
Compressor short cycling
Metering device restriction
Low refrigerant charge

Correct answer: Condenser fan motor failure or reduced airflow

A faulty or undersized condenser fan results in inadequate heat rejection, causing head pressure to rise and trip the high-pressure switch.

Question 18: How does dehumidification occur in a typical residential split-system air conditioner?

Warm humid air is chilled below its dew point over the evaporator coil, causing moisture to condense on the coil (Correct answer)
The blower wheel centrifuges moisture droplets out of the airstream by centrifugal force
A desiccant wheel inside the air handler absorbs water vapor from the airstream
Refrigerant vapor directly absorbs water molecules from supply air passing through the coil

Correct answer: Warm humid air is chilled below its dew point over the evaporator coil, causing moisture to condense on the coil

When warm humid air contacts the cold evaporator coil (below the air's dew point), water vapor condenses on the coil surface and drains away, reducing indoor humidity.

Question 19: Under current EPA rules, which types of refrigerants are classified as 'non-exempt substitutes' and may be subject to use restrictions under the SNAP program?

All HFCs regardless of application
Only refrigerants with a GWP above 2,500
Only ozone-depleting CFCs and HCFCs
Refrigerants listed as unacceptable or acceptable with use conditions for specific applications (Correct answer)

Correct answer: Refrigerants listed as unacceptable or acceptable with use conditions for specific applications

The EPA SNAP (Significant New Alternatives Policy) program evaluates substitutes and may list them as unacceptable or acceptable only under specific use conditions, restricting their application.

Question 20: On a residential split-system schematic, which wire color is most commonly used for the 24V 'Y' (cooling) signal from thermostat to air handler?

Yellow (Correct answer)
White
Green
Red

Correct answer: Yellow

The Y terminal carries the cooling call signal, and by industry convention this wire is yellow, though actual installations should always be verified against the wiring diagram.

Question 21: What is the purpose of the reversing valve in a heat pump system?

To equalize high and low side pressures during shutdown
To prevent refrigerant from flowing back through the compressor
To regulate refrigerant flow based on outdoor temperature
To reverse refrigerant flow direction, switching between heating and cooling modes (Correct answer)

Correct answer: To reverse refrigerant flow direction, switching between heating and cooling modes

The reversing valve redirects refrigerant flow so the outdoor coil becomes the evaporator in cooling mode and the condenser in heating mode, or vice versa.

Question 22: A technician recovers refrigerant into a recovery cylinder that is already at 80% liquid capacity. What should be done next?

Vent the vapor space to make room
Heat the cylinder to compress the liquid further
Stop recovery and use a new or properly sized cylinder (Correct answer)
Continue recovery — 80% is safe for most cylinders

Correct answer: Stop recovery and use a new or properly sized cylinder

Recovery cylinders must never be filled beyond 80% liquid capacity to allow for thermal expansion and prevent dangerous pressure buildup.

Question 23: What is the correct sequence for making a brazed refrigerant line connection?

Heat joint, insert tube, apply flux, braze
Insert tube, apply flux, heat joint to brazing temp, apply filler (Correct answer)
Insert tube, heat joint, apply filler, apply flux
Apply filler, heat joint, insert tube, cool quickly

Correct answer: Insert tube, apply flux, heat joint to brazing temp, apply filler

The proper sequence is to insert the tube fully, apply flux if needed, heat the joint evenly to brazing temperature, then apply the filler rod at the joint.

Question 24: What is the primary reason for insulating the suction line on a new residential AC installation?

To protect the copper from UV degradation outdoors
To prevent condensation on the line and maintain superheat to the compressor (Correct answer)
To increase suction pressure and system efficiency
To reduce noise transmission through the line set

Correct answer: To prevent condensation on the line and maintain superheat to the compressor

Suction line insulation prevents condensation (which causes dripping and potential mold) and reduces heat gain into the cold suction vapor, preserving superheat to protect the compressor.

Question 25: Which refrigerant is classified as an HFC and is commonly used in residential air conditioning systems manufactured after 2010?

R-410A (Correct answer)
R-22
R-502
R-12

Correct answer: R-410A

R-410A is an HFC refrigerant that replaced R-22 in residential AC systems due to its zero ozone depletion potential.

Question 26: A technician finds that a condenser fan motor runs but the compressor does not start and hums loudly. The MOST likely electrical cause is:

Failed high-pressure switch
Loose thermostat R wire
Open run capacitor for the compressor (Correct answer)
Faulty contactor holding coil

Correct answer: Open run capacitor for the compressor

A failed run capacitor reduces starting torque, causing the compressor to hum and fail to start while still drawing locked-rotor amperage.

Question 27: While troubleshooting a residential system, a technician finds oil stains near the compressor service valves. What does this indicate?

Excess refrigerant charge
Normal compressor lubrication weeping
Condenser coil corrosion
A refrigerant and oil leak at that location (Correct answer)

Correct answer: A refrigerant and oil leak at that location

Oil stains near refrigerant connections indicate a refrigerant leak, since oil travels with refrigerant and deposits at leak points.

Question 28: What is the function of a hard start kit (potential relay and start capacitor) shown in a schematic?

To soft-start the condenser fan motor
To boost starting torque and reduce locked-rotor amperage duration (Correct answer)
To provide surge protection during lightning storms
To regulate refrigerant pressure during startup

Correct answer: To boost starting torque and reduce locked-rotor amperage duration

A hard start kit adds extra capacitance to boost starting torque, allowing the compressor to start under load and reducing the time spent at high locked-rotor amperage.

Question 29: What is the purpose of the time-delay relay (TDR) found in some residential AC control circuits?

Delays thermostat response to prevent rapid temperature swings
Prevents compressor short-cycling by enforcing a minimum off time between starts (Correct answer)
Delays transformer energization after a power outage
Controls the speed of the condenser fan motor

Correct answer: Prevents compressor short-cycling by enforcing a minimum off time between starts

A TDR enforces a compressor off-delay (typically 3–5 minutes) to allow pressures to equalize, preventing motor damage from trying to start against unequalized head pressure.

Question 30: What is subcooling in a refrigeration system?

Cooling the compressor discharge gas below ambient
Lowering indoor humidity below the dew point
Chilling the refrigerant liquid below its condensing saturation temperature (Correct answer)
Reducing suction pressure at the compressor inlet

Correct answer: Chilling the refrigerant liquid below its condensing saturation temperature

Subcooling is the number of degrees the liquid refrigerant is cooled below its saturation condensing temperature, improving system efficiency.

Question 31: In a schematic, what does a variable resistor (potentiometer) symbol indicate about a component?

The component's resistance can be adjusted, such as a fan speed control (Correct answer)
The component measures resistance in the circuit
The component has a fixed resistance value
The component converts AC to DC power

Correct answer: The component's resistance can be adjusted, such as a fan speed control

A potentiometer symbol (resistor with an arrow) indicates an adjustable resistance, commonly used in fan speed controls, thermostat anticipators, or sensor calibration circuits.

Question 32: After a thunderstorm, a residential system has no cooling. The indoor fan operates, but the outdoor unit does not run. What is the most likely first item to check?

Refrigerant charge
Contactor coil voltage
Thermostat wiring
Outdoor unit disconnect and fuses or circuit breaker (Correct answer)

Correct answer: Outdoor unit disconnect and fuses or circuit breaker

Power surges from storms frequently blow fuses or trip breakers to the outdoor unit, making electrical supply the first item to verify.

Question 33: On a psychrometric chart, wet-bulb temperature lines run in which direction?

Horizontally across the chart
Vertically parallel to the dry-bulb temperature axis
Diagonally downward from the saturation curve toward the lower right (Correct answer)
In concentric arcs around the origin point

Correct answer: Diagonally downward from the saturation curve toward the lower right

Wet-bulb temperature lines slope diagonally downward from upper left to lower right on a psychrometric chart and nearly coincide with lines of constant enthalpy.

Question 34: What happens to relative humidity when air temperature increases while the moisture content stays the same?

Relative humidity immediately reaches 100% at elevated temperatures
Relative humidity decreases because warmer air can hold more moisture (Correct answer)
Relative humidity stays constant because no moisture was added or removed
Relative humidity increases because warmer air holds less moisture

Correct answer: Relative humidity decreases because warmer air can hold more moisture

As temperature rises, the moisture-holding capacity of air increases, so with unchanged absolute moisture content the relative humidity (a ratio) decreases.

Question 35: Nitrogen should be flowing through refrigerant lines during brazing primarily to:

Increase brazing temperature
Reduce silver content needed
Prevent internal oxidation and scale formation (Correct answer)
Cool the joint faster

Correct answer: Prevent internal oxidation and scale formation

Flowing dry nitrogen through the tubing during brazing displaces oxygen and prevents the formation of copper oxide scale inside the lines.

Question 36: Which tool is used to verify that a 240V circuit is correctly wired with both hot legs and a ground, without a neutral?

Manifold gauge set
Capacitance meter
Non-contact voltage tester on each leg and a multimeter leg-to-leg and leg-to-ground (Correct answer)
Clamp-on ammeter

Correct answer: Non-contact voltage tester on each leg and a multimeter leg-to-leg and leg-to-ground

You confirm 240V leg-to-leg and ~120V from each hot leg to ground using a multimeter; a non-contact tester confirms both conductors are energized.

Question 37: A duct system uses a trunk-and-branch layout. What is the primary advantage of this design?

Provides the lowest static pressure of any layout
Easiest to balance airflow to individual rooms
Simplest to fabricate and requires less material than extended plenum (Correct answer)
Eliminates the need for dampers entirely

Correct answer: Simplest to fabricate and requires less material than extended plenum

Trunk-and-branch systems use a central trunk with smaller branch takeoffs, reducing material compared to running full-size ducts to every outlet.

Question 38: A technician is called to decommission an old residential air conditioning unit. The technician successfully recovers the refrigerant into an approved cylinder. According to regulations, what must be done with the decommissioned system?

The lineset can be cut and left open to the atmosphere.
The system can be immediately sent to a landfill.
A notice must be attached stating that the refrigerant has been removed. (Correct answer)
The system must be filled with nitrogen to a pressure of 150 psig.

Correct answer: A notice must be attached stating that the refrigerant has been removed.

Ontario Regulation 463/10 requires that once a system is decommissioned and the refrigerant has been evacuated, a notice must be affixed to it. This notice must state that the refrigerant has been removed and include details such as the date, the technician's name, and their ODP certificate number.

Question 39: What is the primary role of the expansion valve in an air conditioning system?

Control the flow of outdoor air
Reduce refrigerant pressure and temperature (Correct answer)
Condense the refrigerant
Compress the refrigerant

Correct answer: Reduce refrigerant pressure and temperature

The expansion valve, also known as a metering device, is positioned between the condenser and the evaporator. Its critical role is to precisely control the flow of liquid refrigerant into the evaporator and, more importantly, to reduce its pressure and temperature. This pressure drop causes the refrigerant to flash into a cold, low-pressure mixture of liquid and vapor, ready to absorb heat.

Question 40: When making a brazed joint, the correct way to apply the brazing rod is:

Pre-tin both pieces with filler before assembly
Touch the rod directly to the torch flame to melt it onto the joint
Apply the rod to the back side of the joint only
Hold the rod at the joint and let the heat of the base metal melt the filler (Correct answer)

Correct answer: Hold the rod at the joint and let the heat of the base metal melt the filler

The base metal's heat should melt the brazing rod at the joint, allowing capillary action to draw the filler into the gap for full penetration.

Question 41: A technician discovers that a system's operating pressures are within normal range, but the compressor body is abnormally hot. What should be evaluated?

Discharge line insulation
Refrigerant charge level
Condenser coil surface temperature
Suction gas returning to cool the compressor, motor winding integrity, and ambient temperature (Correct answer)

Correct answer: Suction gas returning to cool the compressor, motor winding integrity, and ambient temperature

Overheating compressors with normal pressures may suffer from inadequate suction gas cooling, high ambient temperature, or motor winding problems causing excess heat generation.

Question 42: In a residential AC electrical schematic, which component is responsible for protecting the compressor from damage if there is a refrigerant leak causing suction pressure to drop to an unsafe level?

The circuit breaker.
The run capacitor.
The low-pressure switch. (Correct answer)
The high-pressure switch.

Correct answer: The low-pressure switch.

The low-pressure switch is a safety device installed on the suction side of the system. If the refrigerant pressure drops below a preset limit, which can happen during a leak, the switch opens the control circuit to the compressor contactor, shutting it down to prevent damage from running without sufficient refrigerant.

Question 43: When a duct passes through an unconditioned space, the minimum insulation R-value required by most US energy codes is:

R-6
R-4
R-8 (Correct answer)
R-13

Correct answer: R-8

IECC and most state energy codes require a minimum of R-8 insulation on ducts located in unconditioned spaces such as attics and crawlspaces.

Question 44: According to ASHRAE 15, a machinery room must have a refrigerant detector that activates ventilation at what concentration threshold?

25% of the IDLH value
At any detectable concentration above 0 ppm
The detector must activate at the TLV or lower (Correct answer)
At the lower flammability limit (LFL) only

Correct answer: The detector must activate at the TLV or lower

ASHRAE 15 requires that the refrigerant detector activate emergency ventilation at or below the refrigerant's TLV (Threshold Limit Value) to protect occupants before dangerous concentrations are reached.

Question 45: When a residential air conditioner produces adequate cooling but the homeowner reports unusually high humidity indoors, what should the technician evaluate?

Evaporator coil temperature and airflow rate (Correct answer)
Refrigerant charge level
Compressor valve efficiency
Condenser fan blade pitch

Correct answer: Evaporator coil temperature and airflow rate

Excessive airflow or elevated evaporator coil temperature reduces the system's ability to condense and drain moisture from the air.

Question 46: What is the typical temperature differential (TD) across a properly functioning residential evaporator coil?

30–40°F
8–12°F
2–5°F
16–22°F (Correct answer)

Correct answer: 16–22°F

A properly charged residential system typically produces a 16–22°F temperature drop across the evaporator coil from return to supply air.

Question 47: A residential condenser fan motor has three leads labeled common, start, and run. Which winding has the highest resistance?

Both windings are equal
Start winding (Correct answer)
Run winding
Common lead

Correct answer: Start winding

The start winding is made of thinner wire with more turns, giving it higher resistance than the run winding.

Question 48: In modern, high-efficiency residential air handlers, which type of motor is commonly used to provide variable airflow and improve system efficiency?

Shaded-pole motor
Electronically Commutated Motor (ECM) (Correct answer)
Permanent Split Capacitor (PSC) motor
Capacitor-start induction-run motor

Correct answer: Electronically Commutated Motor (ECM)

Electronically Commutated Motors (ECMs) are brushless DC motors with integrated electronics that allow for precise, variable speed control. This capability enables the air handler to adjust airflow based on demand, significantly increasing energy efficiency and improving comfort and humidity control compared to older PSC motors.

Question 49: A high-pressure switch in a residential AC system is wired in series with the:

Compressor contactor coil circuit (Correct answer)
Low-voltage transformer primary
Condenser fan motor run capacitor
Indoor blower relay

Correct answer: Compressor contactor coil circuit

The high-pressure switch opens the control circuit to de-energize the contactor coil, shutting off the compressor when discharge pressure exceeds a safe limit.

Question 50: A residential AC system is short-cycling on high pressure. Which maintenance action should the technician perform FIRST?

Add refrigerant to the system
Replace the compressor
Check and clean the condenser coil for blockage or dirt (Correct answer)
Replace the high-pressure switch

Correct answer: Check and clean the condenser coil for blockage or dirt

A dirty or blocked condenser coil reduces heat rejection, causing high-side pressure to rise and the system to trip on the high-pressure limit.

Question 51: What is the purpose of the 'nameplate data' requirement under UL 1995 for listed heating and cooling equipment?

To provide marketing information approved by the manufacturer
To certify that the refrigerant charge has been verified at the factory
To give installers and inspectors essential safety and operating data required for proper installation (Correct answer)
To document the serial number for warranty tracking purposes only

Correct answer: To give installers and inspectors essential safety and operating data required for proper installation

UL 1995 requires nameplate data to convey critical installation and safety information — including voltage, ampacity, refrigerant type, and charge — so that installers and inspectors can verify code compliance.

Question 52: When is a mechanical room required by ASHRAE 15 for a residential refrigeration system using a Group A1 refrigerant like R-410A?

Only when the system is installed in a basement
Never; Group A1 refrigerants are exempt from mechanical room requirements (Correct answer)
Always, regardless of charge size
When the system charge exceeds the room quantity limit (RQL)

Correct answer: Never; Group A1 refrigerants are exempt from mechanical room requirements

ASHRAE 15 exempts Group A1 refrigerants (low toxicity, nonflammable) from mandatory mechanical room requirements because they pose minimal risk in occupied spaces.

Question 53: How often should the condenser coils be cleaned to maintain optimal performance?

Every two months
Once every five years
Once a year (Correct answer)
Only when the system fails

Correct answer: Once a year

The outdoor condenser coils are exposed to dirt, leaves, grass clippings, and other debris, which can accumulate and reduce their ability to dissipate heat. Cleaning them at least once a year, typically in the spring before the cooling season begins, ensures optimal heat transfer efficiency, prevents system strain, and extends the unit's lifespan.

Question 54: What duct material is NOT recommended for use in return air systems because it can off-gas harmful compounds when exposed to the airstream?

Galvanized spiral duct
Sheet metal
Fiberglass duct board
Asbestos-containing duct insulation (Correct answer)

Correct answer: Asbestos-containing duct insulation

Asbestos-containing duct insulation is prohibited because asbestos fibers can be entrained in the airstream and inhaled by occupants.

Question 55: A technician is recovering R-410A from a residential system using a recovery machine. The recovery cylinder, which has a water capacity (WC) of 47.6 lbs and a tare weight (TW) of 18 lbs, is placed on a digital scale. What is the maximum final weight on the scale before the recovery process must be stopped?

47.6 lbs
56.1 lbs (Correct answer)
65.6 lbs
38.1 lbs

Correct answer: 56.1 lbs

To prevent dangerous hydrostatic pressure from liquid expansion, recovery cylinders must not be filled with liquid refrigerant beyond 80% of their water capacity. First, calculate the maximum refrigerant weight: 47.6 lbs (WC) * 0.80 = 38.08 lbs. Then, add the cylinder's tare weight (empty weight) to find the maximum gross weight: 38.08 lbs + 18 lbs (TW) = 56.08 lbs. The closest and safest answer is 56.1 lbs.

Question 56: What does the symbol for a fuse look like on a standard electrical schematic?

A rectangle with a wavy line or S-curve inside (Correct answer)
A triangle pointing upward
A circle with an X inside
Two parallel lines of unequal length

Correct answer: A rectangle with a wavy line or S-curve inside

A fuse is represented on schematics as a rectangle containing a wavy or S-shaped line, symbolizing the fusible element inside.

Question 57: A technician is performing a leak check on a newly installed system using an electronic leak detector. Where should they check FIRST for common installation-related leaks?

The electrical wiring terminals
The ductwork supply registers
Brazed joints, flare connections, and Schrader valve cores (Correct answer)
The air filter slot

Correct answer: Brazed joints, flare connections, and Schrader valve cores

Brazed joints, flare connections, and Schrader valve cores are the most common locations for refrigerant leaks after a new installation and should be the first points checked.

Question 58: What is the primary purpose of adding superheat to the refrigerant vapor before it leaves the evaporator?

To increase the efficiency of the condenser coil.
To lower the pressure of the refrigerant before condensation.
To increase the cooling capacity of the system.
To ensure only vapor enters the compressor, preventing damage. (Correct answer)

Correct answer: To ensure only vapor enters the compressor, preventing damage.

Superheat is the heat added to the refrigerant after it has completely boiled into a vapor. Its main purpose is to ensure that no liquid droplets travel back to the compressor, as liquid cannot be compressed and can cause severe mechanical damage (slugging).

Question 59: What is the function of a hard start kit (potential relay and start capacitor) added to an existing AC compressor?

Increase starting torque to help the compressor start under difficult conditions (Correct answer)
Reduce running amperage during normal operation
Replace the dual run capacitor permanently
Provide overcurrent protection to the compressor

Correct answer: Increase starting torque to help the compressor start under difficult conditions

A hard start kit adds extra starting torque, which is helpful when supply voltage is low, refrigerant pressures are unequalized, or the compressor is aging.

Question 60: When using an electronic leak detector and no leak is found at suspected areas, what technique should the technician use next?

Replace the entire refrigerant circuit
Use UV dye and a UV light to locate the leak (Correct answer)
Recover all refrigerant and pressure test with nitrogen
Increase system pressure by adding refrigerant

Correct answer: Use UV dye and a UV light to locate the leak

UV dye inspection is an effective secondary method to locate leaks that electronic detectors may miss, especially slow or intermittent leaks.

Question 61: Which of the following describes the state of the refrigerant as it enters the metering device in a properly functioning air conditioning system?

Low-pressure, low-temperature liquid
High-pressure, warm liquid (Correct answer)
High-pressure, high-temperature vapor
Low-pressure, superheated vapor

Correct answer: High-pressure, warm liquid

After leaving the condenser, the refrigerant has rejected heat to the outdoors and has condensed from a high-pressure vapor into a high-pressure, warm liquid. This subcooled liquid then flows to the metering device.

Question 62: Before replacing a faulty blower motor in a residential air handler, which of the following represents the most critical and complete safety procedure?

Turn off the thermostat and pull the outdoor disconnect.
Wear insulated gloves and use non-conductive tools.
Isolate, lock out, and tag the circuit breaker controlling the air handler. (Correct answer)
Turn off the circuit breaker for the air handler at the main electrical panel.

Correct answer: Isolate, lock out, and tag the circuit breaker controlling the air handler.

The most critical safety procedure is to de-energize the equipment and ensure it cannot be accidentally re-energized. This is accomplished by turning off the correct circuit breaker, applying a personal lock (lockout), and attaching a tag (tagout) to inform others that the circuit is being serviced. This prevents accidental startup and electrical shock.

Question 63: What is relative humidity (RH)?

The temperature difference between wet-bulb and dry-bulb readings
The ratio of actual moisture content to the maximum moisture air can hold at that temperature (Correct answer)
The temperature at which condensation forms on interior surfaces
The actual mass of water vapor in air measured in grains per pound of dry air

Correct answer: The ratio of actual moisture content to the maximum moisture air can hold at that temperature

Relative humidity is the ratio of actual water vapor pressure to saturation water vapor pressure at the same temperature, expressed as a percentage.

Question 64: What occurs to the refrigerant in the condenser coil during the refrigeration cycle?

It decreases in pressure
It releases heat and condenses into a liquid (Correct answer)
It absorbs heat and vaporizes
It expands and cools

Correct answer: It releases heat and condenses into a liquid

In the condenser coil, the high-pressure, high-temperature refrigerant vapor releases the heat it absorbed from the indoor air to the cooler outdoor air. As it loses heat, the refrigerant undergoes a phase change, condensing back into a high-pressure liquid. This process is essential for the continuous cycle of heat transfer.

Question 65: A technician is called for a no-cool complaint and finds the suction pressure is unusually low, near 0 psig, and the head pressure is also significantly lower than normal. The suction line at the outdoor unit feels warm to the touch. What is the most likely cause?

A major system overcharge
Non-condensables in the system
Severe refrigerant leak or empty system (Correct answer)
Failed condenser fan motor

Correct answer: Severe refrigerant leak or empty system

When a system has lost most or all of its refrigerant, there is very little medium to absorb heat in the evaporator or reject it in the condenser. This results in extremely low pressures on both the high and low sides. The lack of refrigerant means no cooling is occurring, leading to a warm suction line.

Question 66: What is the first step when installing a new residential air conditioning system?

Charging the refrigerant system
Testing the airflow
Connecting the electrical wiring
Conducting a site inspection (Correct answer)

Correct answer: Conducting a site inspection

Before installing a new AC system, a thorough site inspection is the crucial first step. This involves assessing the home's layout, existing ductwork, electrical capacity, and potential locations for indoor and outdoor units. A proper inspection ensures the correct system size is chosen, identifies any necessary modifications, and plans for an efficient and safe installation.

Question 67: Which terminal on a residential heat pump thermostat controls the reversing valve for switching between heating and cooling modes?

O or B (Correct answer)
E
Y2
W2

Correct answer: O or B

The O or B terminal controls the reversing valve solenoid; O energizes the valve in cooling mode (most brands), while B energizes it in heating mode (Rheem/Ruud).

Question 68: What does the term 'psychrometrics' refer to in HVAC?

The study of chemical reactions in refrigerants
The measurement of refrigerant pressures in a system
The study of thermodynamic properties of moist air (Correct answer)
The analysis of duct static pressure losses

Correct answer: The study of thermodynamic properties of moist air

Psychrometrics is the engineering science that studies the thermodynamic properties of moist air — mixtures of dry air and water vapor.

Question 69: A customer reports their AC is blowing air, but it is not cool. The technician verifies the indoor blower and outdoor condenser fan are running, but the compressor is not. A distinct 'clicking' sound is heard from the outdoor unit every few minutes. The 'clicking' is most likely caused by which component?

The compressor's internal overload protector (Correct answer)
The thermostat cycling on and off
The main power disconnect
A faulty condenser fan motor relay

Correct answer: The compressor's internal overload protector

The symptoms describe a compressor that is attempting to start but failing, causing a high amperage draw and significant heat buildup. The 'clicking' sound is characteristic of the thermal overload protector opening the circuit to protect the motor. After a few minutes, it cools, resets ('clicks' closed), and the compressor tries to start again, repeating the cycle.

Question 70: When checking for a refrigerant non-condensable gas contamination, what symptom would be most evident?

Very low subcooling with normal superheat
Low suction pressure and normal head pressure
High head pressure that does not correspond to expected saturation temperature (Correct answer)
Compressor short cycling on low pressure

Correct answer: High head pressure that does not correspond to expected saturation temperature

Non-condensable gases (such as air or nitrogen) cannot condense in the condenser, causing abnormally high head pressure relative to the saturation temperature.

Question 71: Which document must an HVAC technician have to legally purchase refrigerants regulated under EPA Section 608?

An OSHA 10-hour card
A state contractor's license
A manufacturer's authorization letter
An EPA Section 608 technician certification (Correct answer)

Correct answer: An EPA Section 608 technician certification

EPA Section 608 requires technicians who purchase refrigerants in containers larger than 2 lbs to hold a valid Section 608 certification.

Question 72: A technician installs an auxiliary drain pan under an attic air handler. What additional safety device should be wired into the system to prevent ceiling water damage?

Condensate pump with float switch
Overflow guard on the primary P-trap
Auxiliary drain pan float switch wired to interrupt cooling (Correct answer)
High-limit thermostat on the heat exchanger

Correct answer: Auxiliary drain pan float switch wired to interrupt cooling

A float switch in the auxiliary pan is wired to interrupt the cooling circuit so the system shuts down before the secondary pan overflows and damages the ceiling.

Question 73: Which of the following is a safety control designed to shut down the compressor if the refrigerant pressure on the high side becomes dangerously high?

High-pressure switch (Correct answer)
Low-pressure switch
Crankcase heater
Thermostatic expansion valve (TXV)

Correct answer: High-pressure switch

The high-pressure switch is a safety device that monitors the discharge pressure of the compressor. If the pressure exceeds a preset limit (often due to a dirty condenser coil or failed fan motor), the switch opens the control circuit, de-energizing the contactor and stopping the compressor to prevent catastrophic damage.

Question 74: During a maintenance check, a technician observes frost forming on the evaporator coil, and the suction line is sweating heavily all the way back to the compressor. Manifold gauge readings show normal head pressure but higher-than-normal suction pressure. Which of the following is the most probable cause?

A stuck-open metering device
Low refrigerant charge
A restricted liquid line filter drier
Poor indoor airflow across the evaporator (Correct answer)

Correct answer: Poor indoor airflow across the evaporator

Insufficient airflow over the evaporator coil, often caused by a clogged filter or dirty coil, reduces the amount of heat being absorbed by the refrigerant. This causes the refrigerant's saturation temperature to drop below freezing, leading to frost. The reduced heat load also means the refrigerant doesn't boil off as quickly, resulting in a higher-than-normal suction pressure and low superheat (flooding).

Question 75: A homeowner reports water dripping from the indoor air handler. The evaporator coil is clear and not frosted. What is the most likely cause?

Clogged condensate drain line (Correct answer)
Leaking suction line insulation
Refrigerant overcharge
Failed indoor blower motor

Correct answer: Clogged condensate drain line

A blocked condensate drain prevents condensate from flowing away from the unit, causing it to overflow and drip from the air handler.

Question 76: When refrigerant is recovered from a system and later sent to a reclaimer, the reclaimer is required by EPA to:

Return the reclaimed refrigerant or equivalent virgin refrigerant to the sender (Correct answer)
Hold the refrigerant for 30 days to test for contamination before return
Blend the recovered refrigerant with virgin stock before return
Destroy all recovered refrigerant and provide a certificate of destruction

Correct answer: Return the reclaimed refrigerant or equivalent virgin refrigerant to the sender

Certified reclaimers must return to the sender an equivalent quantity of refrigerant meeting AHRI 700 purity standards, though not necessarily the exact same molecules.

Question 77: What evacuation level is required before opening a system for major repairs on equipment manufactured after November 15, 1993, using a recovery machine manufactured after that same date?

10 inches Hg vacuum
4 inches Hg vacuum (Correct answer)
0 psig
15 inches Hg vacuum

Correct answer: 4 inches Hg vacuum

For equipment manufactured after November 15, 1993, using a post-1993 recovery machine, the required evacuation level before major repairs is 4 inches of mercury vacuum.

Question 78: When reading a pictorial wiring diagram, a wire shown going to a splice or junction with a dot indicates:

An open circuit at that point
A test point for measuring voltage
An electrical connection between crossing or meeting wires (Correct answer)
A wire that continues to the next component without making connection

Correct answer: An electrical connection between crossing or meeting wires

A solid dot at a wire junction on a schematic indicates an electrical connection is made at that point, as opposed to wires that cross without a dot (no connection).

Question 79: During a residential AC installation, the outdoor condenser unit should be elevated above grade to:

Reduce compressor vibration noise
Reduce refrigerant pressure drop
Prevent flooding and allow air circulation beneath the unit (Correct answer)
Lower the center of gravity for stability

Correct answer: Prevent flooding and allow air circulation beneath the unit

Elevating the condenser on a pad protects it from standing water and allows proper airflow under the unit.

Question 80: In a residential AC ladder diagram, each horizontal 'rung' of the ladder represents:

A single wire in the wiring harness
A separate voltage level in the system
A different refrigerant circuit zone
An individual control circuit path from power to neutral (or common) (Correct answer)

Correct answer: An individual control circuit path from power to neutral (or common)

Each rung of a ladder diagram is a complete control circuit path showing the series/parallel arrangement of contacts and coils between the two power rails (L1 and L2/Neutral).

Question 81: After a new system installation, a technician performs a standing vacuum test and observes the micron gauge rise from 300 to 1,500 microns over 15 minutes with valves closed. What does this indicate?

The vacuum pump is functioning correctly
Moisture or a refrigerant leak is present in the system (Correct answer)
Nitrogen from the pressure test is still off-gassing
The system is properly dehydrated and leak-free

Correct answer: Moisture or a refrigerant leak is present in the system

A rising micron level during a standing vacuum test indicates either a leak allowing air/moisture in, or residual moisture boiling off inside the system.

Question 82: A technician measures a suction pressure equivalent to 40°F saturation temperature. The suction line temperature is 50°F. What is the superheat?

40°F
10°F (Correct answer)
90°F
50°F

Correct answer: 10°F

Superheat equals the actual suction line temperature (50°F) minus the saturation temperature at suction pressure (40°F), which is 10°F.

Question 83: What does it mean when a contactor shows pitted or burned contact surfaces?

The contacts are properly broken in and will perform better
The contacts have experienced arcing and should be replaced to prevent unreliable operation (Correct answer)
The compressor is drawing below normal amperage
The contactor coil voltage is too high

Correct answer: The contacts have experienced arcing and should be replaced to prevent unreliable operation

Pitted contacts result from electrical arcing during switching, which degrades contact surface quality and increases resistance, leading to heat buildup and potential failures.

Question 84: What does an elevated wet-bulb temperature at the evaporator inlet indicate?

Blocked condensate drain
High indoor humidity or high sensible heat ratio (Correct answer)
Low indoor humidity
Refrigerant overcharge in the evaporator

Correct answer: High indoor humidity or high sensible heat ratio

A higher wet-bulb temperature at the coil inlet indicates more moisture (latent heat) in the air, increasing the total load on the evaporator.

Question 85: Under current EPA venting prohibition rules, which substance may still legally be vented to atmosphere under specific conditions?

Nitrogen used to pressurize a system for leak testing (Correct answer)
R-22
R-134a
R-410A

Correct answer: Nitrogen used to pressurize a system for leak testing

Nitrogen is not a refrigerant and is not subject to the EPA venting prohibition; it may be vented after leak testing or pressurization procedures.

Question 86: What is the significance of measuring refrigerant pressure at both the high-side and low-side service ports simultaneously during diagnosis?

It determines the age of the compressor
It allows calculation of pressure differential to assess compressor performance and refrigerant state (Correct answer)
It identifies the brand of refrigerant in the system
It verifies the accuracy of the gauge manifold

Correct answer: It allows calculation of pressure differential to assess compressor performance and refrigerant state

Simultaneous high- and low-side pressure readings allow the technician to calculate compression ratio and compare system pressures to expected values for the given conditions.

Question 87: What is the primary function of an evaporator coil in an air conditioning system?

Regulate refrigerant flow
Compress refrigerant to high pressure
Release heat to outdoor air
Absorb heat from indoor air (Correct answer)

Correct answer: Absorb heat from indoor air

The evaporator coil is a crucial component located inside the home's air handler. As warm indoor air passes over its cold surface, the liquid refrigerant inside absorbs heat and vaporizes. This process effectively removes heat and humidity from the indoor environment, cooling the air before it is recirculated.

Question 88: What is the primary purpose of a metering device in a refrigeration circuit?

To reduce refrigerant pressure and control flow into the evaporator (Correct answer)
To filter moisture from the refrigerant
To compress the refrigerant vapor
To transfer heat from the refrigerant to outdoor air

Correct answer: To reduce refrigerant pressure and control flow into the evaporator

The metering device drops refrigerant pressure and regulates flow into the evaporator, enabling it to absorb heat effectively.

Question 89: A pressure transducer shown in an AC schematic differs from a pressure switch in that it:

Is only used on commercial equipment, not residential
Measures temperature rather than pressure
Provides a continuously variable analog or digital output proportional to the refrigerant pressure (Correct answer)
Only opens or closes a circuit at one set pressure

Correct answer: Provides a continuously variable analog or digital output proportional to the refrigerant pressure

A pressure transducer outputs a variable signal (voltage or current) proportional to pressure, allowing precise monitoring, while a pressure switch only has an open/closed output at a fixed setpoint.

Question 90: When sizing the refrigerant line set for a residential split system, the technician should consult:

The equipment manufacturer's installation manual for approved line sizes and lengths (Correct answer)
ASHRAE Standard 62.1 only
NEC Table 310 for conductor ampacity
Any standard copper tubing chart

Correct answer: The equipment manufacturer's installation manual for approved line sizes and lengths

Manufacturers specify maximum and minimum line lengths and required line sizes to maintain proper oil return and refrigerant charge for their equipment.

Question 91: When installing ductwork for a new residential AC system, what is the purpose of using mastic sealant instead of standard duct tape?

Mastic improves thermal insulation of the ducts
Mastic is easier to apply in tight spaces
Mastic provides a durable, long-lasting airtight seal that duct tape cannot maintain over time (Correct answer)
Mastic is required only on return ducts, not supply ducts

Correct answer: Mastic provides a durable, long-lasting airtight seal that duct tape cannot maintain over time

Mastic sealant creates a permanent, flexible, airtight bond at duct joints, whereas standard duct tape degrades and loses adhesion over time, allowing air leaks.

Question 92: A supply register is rated at 0.10 inches w.g. pressure drop at 150 CFM. If airflow increases to 200 CFM, approximately what is the new pressure drop?

0.13 in. w.g.
0.30 in. w.g.
0.18 in. w.g. (Correct answer)
0.22 in. w.g.

Correct answer: 0.18 in. w.g.

Pressure drop varies with the square of airflow change; (200/150)² × 0.10 ≈ 0.18 in. w.g.

Question 93: Which control component in a residential AC system senses indoor temperature and signals the system to cycle on or off?

High-pressure switch
Contactor
Transformer
Thermostat (Correct answer)

Correct answer: Thermostat

The thermostat senses indoor ambient temperature and sends a low-voltage signal to the control circuit to energize or de-energize the system.

Question 94: A zoning system with multiple motorized dampers closes all zones simultaneously. What device prevents damage to the air handler from this condition?

A differential pressure switch on the refrigerant circuit
An outdoor air economizer damper
A low-pressure cutout on the evaporator
A barometric relief damper or bypass damper (Correct answer)

Correct answer: A barometric relief damper or bypass damper

A bypass or barometric relief damper allows air to recirculate when all zone dampers are closed, preventing excessively high static pressure from damaging the blower.

Question 95: A technician notices the system cools adequately in the morning but loses capacity significantly in the afternoon heat. Which diagnosis is most consistent with this behavior?

Dirty or blocked condenser coil (Correct answer)
Intermittent thermostat fault
Dirty evaporator coil
Low refrigerant charge

Correct answer: Dirty or blocked condenser coil

A partially blocked condenser coil can handle lighter loads in cooler morning temperatures but cannot reject adequate heat when ambient temperatures peak in the afternoon.

Question 96: A residential air conditioning system is running, but the indoor unit is not blowing cold air. A technician measures the refrigerant state at the outlet of the evaporator coil and finds it is a saturated mixture. What does this condition most likely indicate?

The condenser fan is malfunctioning.
The metering device is allowing too much refrigerant into the evaporator. (Correct answer)
The system is low on refrigerant.
The system is operating with proper superheat.

Correct answer: The metering device is allowing too much refrigerant into the evaporator.

The refrigerant should leave the evaporator as a superheated vapor, meaning it has absorbed enough heat to completely boil off and then some. A saturated mixture (part liquid, part vapor) at the outlet indicates that not all the liquid refrigerant has boiled off, a condition known as 'flooding.' This is often caused by an overfeeding metering device or a severely restricted airflow over the evaporator.

Question 97: Which of the following components is responsible for creating a pressure differential that allows the refrigerant to change from a high-pressure liquid to a low-pressure liquid?

Condenser
Metering Device (Correct answer)
Evaporator
Compressor

Correct answer: Metering Device

The metering device (such as a TXV or capillary tube) creates a restriction in the flow of refrigerant. This restriction causes a significant drop in pressure, which in turn lowers the refrigerant's boiling point before it enters the evaporator.

Question 98: Which duct leakage test measures total system leakage including leakage to conditioned space?

Pressure pan test
Leakage to outside test
Duct blaster total leakage test (Correct answer)
Blower door test

Correct answer: Duct blaster total leakage test

The total leakage test measures all duct leakage regardless of where it occurs, including leaks inside the conditioned envelope.

Question 99: A technician finds the suction line is sweating heavily all the way back to the compressor. What does this indicate?

Refrigerant undercharge
A failed condenser fan motor
Refrigerant overcharge or metering device stuck open, flooding liquid to the compressor (Correct answer)
Normal operation in humid climates

Correct answer: Refrigerant overcharge or metering device stuck open, flooding liquid to the compressor

Heavy sweating along the full suction line back to the compressor indicates refrigerant is returning as liquid, which can cause liquid slugging and compressor damage.

Question 100: How many grains of moisture are in one pound of water?

7,000 grains (Correct answer)
5,040 grains
10,000 grains
1,000 grains

Correct answer: 7,000 grains

There are exactly 7,000 grains per pound of water; HVAC technicians express air moisture content in grains per pound (GPP) of dry air.

Question 101: A residential system is equipped with a TXV (thermostatic expansion valve). The technician finds high superheat and low suction pressure. What should be inspected?

Discharge line temperature
TXV bulb mounting and charge, and refrigerant charge level (Correct answer)
Compressor discharge valve
Condenser inlet temperature

Correct answer: TXV bulb mounting and charge, and refrigerant charge level

A TXV that is underfeeding the evaporator (due to a faulty bulb, lost bulb charge, or low system charge) causes high superheat and low suction pressure.

Question 102: What is the function of the thermostat in an air conditioning system?

Protect the system from overcurrent
Sense and regulate indoor temperature (Correct answer)
Store electrical energy
Control power supply to motors

Correct answer: Sense and regulate indoor temperature

The thermostat is the primary control interface for an air conditioning system, allowing users to set their desired indoor temperature. It continuously senses the ambient room temperature and, based on the set point, sends signals to the AC unit to turn on or off, thereby regulating the cooling cycle to maintain comfort.

Question 103: While preparing to use a new coil cleaning chemical, a technician observes a WHMIS 2015 pictogram on the label that features a skull and crossbones. What specific hazard does this symbol represent?

Corrosive damage to skin or metals
Acute toxicity (fatal or toxic with short exposure) (Correct answer)
Flammable or combustible material
Biohazardous infectious material

Correct answer: Acute toxicity (fatal or toxic with short exposure)

The skull and crossbones pictogram in WHMIS 2015 is used to indicate that a substance can cause death or acute toxicity with short exposure to small amounts, whether ingested, inhaled, or through skin contact. Technicians must recognize this symbol and consult the Safety Data Sheet (SDS) for specific handling precautions.

Question 104: What is the standard voltage range for the low-voltage control circuit in residential HVAC equipment?

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

Correct answer: 24V AC

Residential HVAC control circuits operate at 24V AC, supplied by the system transformer, to power thermostats, relays, and contactors.

Question 105: What maintenance task ensures efficient airflow in a residential air conditioning system?

Checking refrigerant levels
Inspecting electrical connections
Cleaning or replacing air filters (Correct answer)
Lubricating fan motors

Correct answer: Cleaning or replacing air filters

Air filters are the first line of defense against dust and debris entering the AC system and circulating in the home. Regularly cleaning or replacing them ensures unrestricted airflow, which is vital for the system's efficiency and cooling capacity. Clogged filters restrict airflow, making the system work harder, increasing energy consumption, and reducing indoor air quality.

Question 106: A residential air conditioning system uses a 240V/24V step-down transformer. If the primary side shows 240V but the secondary shows 0V, the MOST likely cause is:

Shorted secondary winding
Incorrect transformer sizing
Open primary winding or blown fuse (Correct answer)
Overloaded control circuit

Correct answer: Open primary winding or blown fuse

An open primary winding or a blown fuse on the primary side will prevent current flow and result in zero secondary voltage output.

Question 107: What is the result of non-condensable gases (such as air) in a refrigerant system?

Lower-than-normal head pressure and reduced compressor amperage
A drop in suction pressure causing evaporator freeze-up
Higher-than-normal head pressure, elevated condenser temperature, and reduced efficiency (Correct answer)
Flooding of the evaporator with liquid refrigerant

Correct answer: Higher-than-normal head pressure, elevated condenser temperature, and reduced efficiency

Non-condensable gases occupy condenser volume and cannot condense, raising head pressure and reducing system efficiency and capacity.

Question 108: A technician performing refrigerant recovery notes the ambient temperature is 95°F and the recovery cylinder is hot to the touch. The correct action is to:

Cool the recovery cylinder with ice or water to lower its pressure and allow continued recovery (Correct answer)
Transfer refrigerant to a second cylinder and discard the hot one
Stop recovery and tag the system as unsafe
Continue recovery — cylinder temperature is not a limiting factor

Correct answer: Cool the recovery cylinder with ice or water to lower its pressure and allow continued recovery

Cooling a hot recovery cylinder reduces its internal pressure, increasing the pressure differential that drives refrigerant flow and improves recovery efficiency.

Question 109: What is the purpose of measuring the temperature difference across a filter-drier (liquid line drier) during operation?

To verify proper superheat
To detect a restriction inside the drier (Correct answer)
To confirm correct refrigerant charge
To measure subcooling accurately

Correct answer: To detect a restriction inside the drier

A notable temperature drop across a filter-drier (more than 1–2°F) indicates the drier is restricted and should be replaced.

Question 110: Which regulation governs the transportation of refrigerant cylinders by road and specifies proper labeling and packaging requirements?

NFPA 55
DOT 49 CFR Part 173 (Correct answer)
EPA 40 CFR Part 82
OSHA 29 CFR 1910.101

Correct answer: DOT 49 CFR Part 173

DOT 49 CFR Part 173 establishes packaging, labeling, and hazmat shipping requirements for compressed gas cylinders including refrigerants transported by road.

Question 111: On a residential air conditioning schematic, what is the function of a contactor?

To control the speed of the indoor blower motor based on the thermostat setting.
To protect the system from operating in dangerously low or high refrigerant pressure conditions.
To use a low-voltage signal to switch the high-voltage power to the compressor and condenser fan motor. (Correct answer)
To step down high voltage to low voltage for the control circuit.

Correct answer: To use a low-voltage signal to switch the high-voltage power to the compressor and condenser fan motor.

A contactor is an electrically controlled switch, similar to a relay but built for higher current loads. In an AC system, the 24-volt signal from the thermostat energizes the contactor's coil, which closes a set of high-voltage contacts, allowing line voltage (e.g., 240V) to power the compressor and condenser fan motor.

Question 112: What does a high superheat AND high subcooling reading together most likely indicate?

Restriction in the liquid line or metering device (Correct answer)
Refrigerant undercharge
Refrigerant overcharge
Compressor valve failure

Correct answer: Restriction in the liquid line or metering device

High subcooling indicates liquid refrigerant is backing up before a restriction, while high superheat indicates insufficient refrigerant reaching the evaporator.

Question 113: What is the maximum recommended length of an unsupported horizontal refrigerant line run before a support hanger is required?

12 feet
8 feet
5 feet (Correct answer)
3 feet

Correct answer: 5 feet

Refrigerant lines should be supported at least every 5 feet horizontally to prevent sagging, vibration damage, and stress on joints.

Question 114: What is the purpose of a duct transition fitting that changes from a rectangular trunk to a round branch?

To filter the air before distribution
To increase system static pressure
To smoothly convert airflow from one duct geometry to another with minimal pressure loss (Correct answer)
To add an access point for duct cleaning

Correct answer: To smoothly convert airflow from one duct geometry to another with minimal pressure loss

Transition fittings are designed to convert duct geometry while minimizing turbulence and pressure drop through gradual shape changes.

Question 115: Which ASHRAE standard sets minimum energy efficiency requirements for residential HVAC equipment in the United States?

ASHRAE 62.1
ASHRAE 34
ASHRAE 90.1 (Correct answer)
ASHRAE 15

Correct answer: ASHRAE 90.1

ASHRAE 90.1 establishes minimum energy efficiency standards for HVAC equipment, and residential equipment must meet these as a baseline for code compliance.

Question 116: According to Ontario Regulation 463/10 under the Environmental Protection Act, what is a key requirement for any person handling or purchasing refrigerants?

They must possess a valid Ozone Depletion Prevention (ODP) certificate. (Correct answer)
They must be accompanied by a licensed journeyperson.
They must renew their trade license annually.
They must hold a valid Gas Technician 2 (G2) license.

Correct answer: They must possess a valid Ozone Depletion Prevention (ODP) certificate.

In Ontario, the law requires that any individual who purchases, handles, or works with refrigerants must have completed an approved environmental awareness training course and hold a valid ODP certificate. This certification must be renewed every five years.

Question 117: What is the purpose of a time-delay relay (TDR) in an AC system schematic?

To reduce current draw during startup
To increase voltage to the compressor
To measure elapsed run time of the unit
To prevent short cycling by delaying compressor restart (Correct answer)

Correct answer: To prevent short cycling by delaying compressor restart

A time-delay relay prevents short cycling by enforcing a minimum off-time before allowing the compressor to restart, protecting it from damage.

Question 118: Which ASHRAE standard provides guidance on acceptable duct leakage rates for residential HVAC systems?

ASHRAE Standard 193
ASHRAE 15
ASHRAE 62.2
ASHRAE 90.1 (Correct answer)

Correct answer: ASHRAE 90.1

ASHRAE 90.1 (and its residential counterpart 90.2) establishes duct leakage requirements as part of energy efficiency standards.

Question 119: A technician is preparing to recover refrigerant from a residential split system. To significantly increase the speed of the recovery process, which of the following actions is most effective?

Ensuring the recovery machine is placed above the outdoor unit.
Recovering only in the vapor phase to protect the recovery machine.
Using the longest possible hoses to reach the service vehicle.
Removing the Schrader valve cores from the service ports. (Correct answer)

Correct answer: Removing the Schrader valve cores from the service ports.

The Schrader valve core is the most significant restriction in the service port. Removing it with a core removal tool before starting the recovery process dramatically increases the flow rate of both liquid and vapor refrigerant, significantly speeding up the job.

Question 120: What flux is most commonly used when brazing copper-to-copper refrigerant joints?

Paste flux with borax base
Acid flux (zinc chloride)
White brazing flux (high-temp)
No flux is needed for copper-to-copper joints (Correct answer)

Correct answer: No flux is needed for copper-to-copper joints

Copper-to-copper joints with high-silver alloy brazing rod do not require flux because the alloy flows well on clean copper without it; flux can leave residues.

Question 121: What indoor relative humidity range does ASHRAE recommend for occupant comfort in residential buildings?

70–80%
10–20%
30–60% (Correct answer)
85–95%

Correct answer: 30–60%

ASHRAE recommends maintaining indoor RH between 30% and 60% to ensure occupant comfort and prevent mold growth or dry-air discomfort.

Question 122: A supply duct system has a design CFM of 1,200. Using the rule of thumb, approximately how many CFM should each 6-inch branch supply?

100 CFM (Correct answer)
75 CFM
125 CFM
50 CFM

Correct answer: 100 CFM

A 6-inch round duct at standard residential velocities typically delivers approximately 100 CFM.

Question 123: Which tool is used to check for refrigerant leaks during system installation?

Vacuum pump
Leak detector (Correct answer)
Thermometer
Manifold gauge set

Correct answer: Leak detector

A leak detector is an essential tool used during and after refrigerant line installation to identify any potential leaks. These electronic devices are designed to sense the presence of refrigerant gases, ensuring the system is sealed properly before charging. Detecting and repairing leaks is crucial for system efficiency and environmental protection.

Question 124: Which safety device protects an ECM blower motor module from power surges and lightning-induced voltage spikes?

Dual run capacitor
Transient voltage surge suppressor (TVSS) or MOV installed on the circuit (Correct answer)
Time-delay fuse in the disconnect
Low-pressure switch

Correct answer: Transient voltage surge suppressor (TVSS) or MOV installed on the circuit

ECM motor modules contain sensitive electronics vulnerable to voltage transients; a TVSS or metal oxide varistor (MOV) clamps surge voltages before they reach the module.

Question 125: Which pressure in an air conditioning system is referred to as the 'high side'?

Pressure between the compressor discharge and the metering device inlet (Correct answer)
Pressure at the evaporator outlet
Pressure at the compressor suction port
Pressure inside the indoor ductwork

Correct answer: Pressure between the compressor discharge and the metering device inlet

The high side spans from compressor discharge through the condenser and liquid line to the inlet of the metering device.

Question 126: Under what condition are dry-bulb and wet-bulb temperatures equal?

When air is at 100% relative humidity (fully saturated) (Correct answer)
When airflow velocity through the duct exceeds 1,000 FPM
When outdoor and indoor dry-bulb temperatures are identical
When the HVAC system is operating at its rated peak efficiency

Correct answer: When air is at 100% relative humidity (fully saturated)

At 100% relative humidity no evaporation occurs from a wet wick, so the wet-bulb thermometer reads the same temperature as the dry-bulb thermometer.

Question 127: Why is refrigerant with a low boiling point ideal for air conditioning systems?

It minimizes energy use
It condenses easily in the evaporator
It prevents overcooling
It ensures efficient heat absorption at room temperature (Correct answer)

Correct answer: It ensures efficient heat absorption at room temperature

Refrigerants with low boiling points are ideal because they can easily vaporize and absorb heat from relatively cool indoor air (around room temperature). This phase change from liquid to gas within the evaporator coil is how the system efficiently extracts heat from the living space. A higher boiling point would mean the refrigerant wouldn't vaporize effectively at typical indoor temperatures.

Question 128: A technician measures a very high condenser entering air temperature of 115°F on a rooftop-adjacent unit. How does this affect system diagnosis?

It causes the evaporator to frost over
It raises suction pressure and improves efficiency
It has no effect on system pressures
It lowers subcooling and reduces system capacity (Correct answer)

Correct answer: It lowers subcooling and reduces system capacity

High entering air temperature to the condenser reduces heat rejection efficiency, raising head pressure and reducing subcooling and overall system capacity.

Question 129: What is the key difference between sensible heat and latent heat in air conditioning?

Sensible heat causes a measurable temperature change; latent heat involves phase change without temperature change (Correct answer)
There is no practical difference — both describe the same heat transfer mechanism
Sensible heat is removed at the condenser; latent heat is added at the compressor
Sensible heat relates to refrigerant flow; latent heat relates to air velocity

Correct answer: Sensible heat causes a measurable temperature change; latent heat involves phase change without temperature change

Sensible heat changes the temperature of air (measurable with a thermometer), while latent heat is absorbed or released during phase changes like evaporation or condensation.

Question 130: A low-pressure switch in an AC schematic is wired in series with the control circuit primarily to:

Protect against high discharge pressure
Cycle the condenser fan at low ambient temperatures
Prevent the blower from operating without refrigerant flow
Shut down the unit if refrigerant loss causes suction pressure to drop below safe limits (Correct answer)

Correct answer: Shut down the unit if refrigerant loss causes suction pressure to drop below safe limits

A low-pressure switch opens the control circuit if suction pressure drops below a set point, indicating refrigerant loss or other abnormal conditions, shutting down the compressor.

Question 131: A 'P-trap' installed in a condensate drain line serves to:

Slow condensate flow to prevent overflow
Maintain a water seal to prevent sewer gases from entering the air handler (Correct answer)
Filter debris from the drain line
Trap refrigerant vapors

Correct answer: Maintain a water seal to prevent sewer gases from entering the air handler

The P-trap's water seal prevents odorous or harmful gases from the drain system from being drawn into the air handler by the unit's negative pressure.

Question 132: Which type of copper tubing is approved for use in refrigerant line sets for residential AC systems?

Type L soft copper plumbing tube
ACR (Air Conditioning and Refrigeration) grade copper (Correct answer)
Galvanized steel tubing
Type M hard-drawn copper

Correct answer: ACR (Air Conditioning and Refrigeration) grade copper

ACR-grade copper tubing is cleaned, dehydrated, and capped at the factory, making it suitable for refrigerant service.

Question 133: Under current DOE regulations effective January 1, 2023, what is the minimum SEER2 requirement for split-system central air conditioners in the Southwest and Southeast U.S.?

15.2 SEER2
14.3 SEER2 (Correct answer)
16.0 SEER2
13.4 SEER2

Correct answer: 14.3 SEER2

DOE's regional standards effective January 2023 require a minimum of 14.3 SEER2 for split-system central ACs sold in the Southeast and Southwest climate regions.

Question 134: According to NEC Article 440, what is the maximum rating of a branch circuit overcurrent device (OCPD) for an air conditioning unit if the nameplate specifies 'Maximum Fuse or HACR Circuit Breaker – 30A'?

40 amperes
30 amperes (Correct answer)
35 amperes
25 amperes

Correct answer: 30 amperes

NEC Article 440 requires that the OCPD not exceed the value marked on the equipment nameplate; if the nameplate states 30A maximum, the installed protective device must be 30A or less.

Question 135: When brazing copper refrigerant lines, what minimum silver content is required for the brazing alloy used in most residential AC applications?

5% silver
15% silver (Correct answer)
45% silver
2% silver

Correct answer: 15% silver

Brazing alloys with at least 15% silver content are typically required for refrigerant line brazing to ensure strong, leak-free joints.

Question 136: A residential split system requires a dedicated 240V, 2-pole circuit breaker. What is the primary reason a 2-pole breaker is required instead of two single-pole breakers?

Code requires 2-pole breakers only for circuits over 30 amps
Single-pole breakers cannot handle 240V circuits
A 2-pole breaker ensures simultaneous disconnection of both hot legs during a fault (Correct answer)
2-pole breakers are cheaper and easier to install

Correct answer: A 2-pole breaker ensures simultaneous disconnection of both hot legs during a fault

A 2-pole breaker trips both hot conductors simultaneously, ensuring the full 240V circuit is de-energized during an overcurrent event for safe protection.

Question 137: During the commissioning of a new residential AC system with a TXV metering device, which charging method provides the most accurate results and is recommended by most manufacturers?

Feeling the suction line temperature by hand to ensure it is 'beer can cold'.
Subcooling method, measured at the liquid line service valve. (Correct answer)
Setting pressures to a standard chart without considering temperatures.
Superheat method, based on indoor wet-bulb and outdoor dry-bulb temperatures.

Correct answer: Subcooling method, measured at the liquid line service valve.

For systems equipped with a Thermostatic Expansion Valve (TXV), the subcooling method is the manufacturer-recommended procedure for accurate charging. The TXV's job is to maintain a constant superheat, so trying to charge by superheat will be inaccurate. Subcooling measures the amount of liquid refrigerant backed up in the condenser, which directly indicates whether the system has the correct refrigerant volume.

Question 138: What is the primary function of a metering device, such as a thermostatic expansion valve (TXV) or a fixed orifice, in a residential air conditioning system?

To create a large pressure drop in the refrigerant. (Correct answer)
To pump the refrigerant through the system.
To filter contaminants from the refrigerant.
To increase the temperature of the liquid refrigerant.

Correct answer: To create a large pressure drop in the refrigerant.

The metering device's main role is to create a significant pressure drop between the high-pressure side (condenser) and the low-pressure side (evaporator) of the system. This rapid pressure reduction causes the high-pressure liquid refrigerant to become a very cold, low-pressure mixture of liquid and vapor, ready to absorb heat in the evaporator.

Question 139: What are the primary negative effects of high indoor relative humidity on occupants?

It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation (Correct answer)
It improves air quality by causing airborne dust particles to clump and settle
It reduces the sensible cooling load by lowering the sensible heat ratio
It increases comfort by preventing static electricity buildup in dry climates

Correct answer: It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation

High indoor humidity fosters mold and mildew, makes occupants feel hotter because perspiration evaporates more slowly, and can aggravate asthma and allergies.

Question 140: While examining a wiring diagram, you see a symbol representing a switch that is held open by a spring and closes when a magnetic field is created by a coil. This symbol most likely represents which of the following components?

A thermostatic expansion valve.
A transformer.
A circuit breaker.
A normally open (NO) relay. (Correct answer)

Correct answer: A normally open (NO) relay.

This describes the basic operation of a normally open (NO) relay or contactor. In its resting state, the contacts are open. When the coil is energized with a control voltage, it creates a magnetic field that pulls the contacts closed, completing a separate circuit.

Question 141: What is the Apparatus Dew Point (ADP) of a cooling coil?

The minimum allowable refrigerant temperature within the evaporator
The effective average surface temperature of the coil at which moisture condenses (Correct answer)
The temperature of condensate water draining from the coil pan
The dew point temperature of the return air stream entering the coil

Correct answer: The effective average surface temperature of the coil at which moisture condenses

ADP is the effective mean surface temperature of a cooling coil — the theoretical temperature at which the coil would saturate leaving air if bypass factor were zero.

Question 142: What is the bypass factor of a cooling coil?

The heat transfer rate through the outer casing of the air handler
The fraction of airflow that passes through the coil without making effective thermal contact (Correct answer)
The ratio of air that bypasses the filter media to total airflow
The amount of refrigerant bypassed around the expansion valve at part load

Correct answer: The fraction of airflow that passes through the coil without making effective thermal contact

Bypass factor is the fraction of air that passes through the coil without meaningfully contacting the coil surface, reducing cooling and dehumidification effectiveness.

Question 143: During a service call, a homeowner reports the system runs continuously but never reaches setpoint. The evaporator coil is partially frosted. What should the technician check first?

Condenser fan motor
Compressor amperage draw
Airflow across the evaporator coil (Correct answer)
Thermostat calibration

Correct answer: Airflow across the evaporator coil

Restricted airflow is the most common cause of evaporator coil frosting and inadequate cooling, and should be checked before electrical components.

Question 144: During a new installation leak check using nitrogen, at what pressure should the technician hold the system before releasing and checking for leaks?

25 psig for 10 minutes
The maximum operating pressure plus 10%
150 psig for 24 hours (Correct answer)
Triple the low-side design pressure

Correct answer: 150 psig for 24 hours

Industry best practice calls for pressurizing with dry nitrogen to 150 psig and holding for at least 24 hours to confirm no pressure drop from leaks.

Question 145: For a residential system serving multiple zones, which device helps balance airflow between branches without mechanical dampers?

Balancing collar (Correct answer)
Splitter damper
Plenum box
Duct board liner

Correct answer: Balancing collar

A balancing collar allows adjustable restriction at branch takeoffs to equalize airflow across multiple runs.

Question 146: Which component in a residential AC system provides low-voltage power to the thermostat and control board?

The outdoor unit contactor
The main disconnect switch
The run capacitor
The 24V step-down control transformer (Correct answer)

Correct answer: The 24V step-down control transformer

The control transformer steps 120V or 240V primary voltage down to 24V AC to power the thermostat, control board, and relay coils.

Question 147: A technician is recovering refrigerant from a system with a charge of 15 lbs. Which EPA vacuum level must be achieved before opening the system for repair?

4 inches Hg vacuum
10 inches Hg vacuum
The system size determines the required recovery vacuum from EPA tables (Correct answer)
0 psig

Correct answer: The system size determines the required recovery vacuum from EPA tables

EPA requires different recovery vacuum levels based on refrigerant type and system charge size; technicians must consult the EPA Section 608 tables for the applicable requirement.

Question 148: What does 'EWT' stand for in HVAC load and equipment performance documentation?

Exhaust Water Temperature
Effective Wet-bulb Temperature
Entering Water Temperature (Correct answer)
Exterior Wall Thickness

Correct answer: Entering Water Temperature

EWT stands for Entering Water Temperature, which is the temperature of water entering a coil or heat exchanger, used in equipment performance ratings.

Question 149: When recovering refrigerant from a system with a known motor burn, the technician should use:

The existing system compressor to push refrigerant into recovery cylinders
A direct-connect hose to the recovery cylinder only — no machine needed
Recovery equipment equipped with an acid-rated filter to capture contaminants (Correct answer)
Standard recovery equipment with a new filter-drier after recovery

Correct answer: Recovery equipment equipped with an acid-rated filter to capture contaminants

Acid-laden refrigerant from a burned compressor requires an acid-rated filter in the recovery machine to protect its components and prevent cross-contamination.

Question 150: What is the effect of an oversized supply duct on room airflow distribution?

Improves throw and mixing in the room
Reduces air velocity causing poor throw and stratification (Correct answer)
Increases static pressure at the register
Has no effect on comfort

Correct answer: Reduces air velocity causing poor throw and stratification

An oversized duct lowers air velocity, reducing register throw and leaving the room with poor air mixing and temperature stratification.

Question 151: A residential system has correct refrigerant charge but the supply air temperature differential (delta-T) is only 10°F instead of the expected 16–22°F. What is the most likely cause?

Excessive airflow across the evaporator (Correct answer)
Liquid line restriction
Refrigerant undercharge
Overcharge of refrigerant

Correct answer: Excessive airflow across the evaporator

Too much airflow across the evaporator reduces the time the air has to exchange heat, resulting in a lower temperature differential.

Question 152: Which type of metering device maintains a constant evaporator outlet superheat regardless of load changes?

Float valve
Fixed orifice
Capillary tube
Thermostatic expansion valve (TXV) (Correct answer)

Correct answer: Thermostatic expansion valve (TXV)

A TXV uses a sensing bulb to modulate refrigerant flow and maintain a nearly constant superheat at the evaporator outlet across varying load conditions.

313D Residential Air Conditioning Systems Mechanic

The 313D Residential Air Conditioning Systems Mechanic Certificate of Qualification exam, administered by Skilled Trades Ontario, validates competency in installing, servicing, and maintaining residential air conditioning and heat pump systems.

150

Questions

240 min

Time Limit

70%

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