313D Residential Air Conditioning Systems Mechanic — Questions and Answers

Question 1: What is the primary purpose of a capacitor in an air conditioning system?

To stabilize voltage fluctuations
To reduce energy consumption
To convert AC to DC
To provide a start-up boost for motors (Correct answer)

Correct answer: To provide a start-up boost for motors

Capacitors in air conditioning systems, particularly start and run capacitors, store electrical energy and release it to provide an initial surge of power to motors like the compressor and fan motors. This boost helps overcome the initial inertia and allows the motors to start efficiently and run smoothly. Without them, motors might struggle to start or draw excessive current.

Question 2: On a blueprint legend, which line type typically indicates a low-voltage control wiring run for the thermostat?

A wavy line
Dashed or dotted line, often labeled 'LV' or 'control' (Correct answer)
A double parallel line
A solid thick line

Correct answer: Dashed or dotted line, often labeled 'LV' or 'control'

Low-voltage control wiring is usually shown as a dashed or dotted line and labeled 'LV' or 'control wiring' in the legend.

Question 3: A residential split system's outdoor disconnect must be located within sight of and within how many feet of the equipment?

25 feet
50 feet (Correct answer)
100 feet
75 feet

Correct answer: 50 feet

The NEC requires the disconnecting means to be within sight of and within 50 feet of the air conditioning equipment it serves.

Question 4: Which federal agency certifies technicians who service, maintain, repair, or dispose of equipment containing refrigerants?

OSHA
NATE
EPA (Correct answer)
DOT

Correct answer: EPA

The U.S. Environmental Protection Agency (EPA) administers the Section 608 technician certification program under the Clean Air Act.

Question 5: A technician is diagnosing a residential AC unit where the condenser fan and compressor are humming but not starting. The technician can easily spin the fan blade by hand. Which of the following components is the most likely cause of this issue?

The dual-run capacitor (Correct answer)
The transformer
The thermostat
The circuit breaker

Correct answer: The dual-run capacitor

A dual-run capacitor provides the necessary starting torque for both the compressor and condenser fan motor. When it fails, the motors receive power but lack the phase-shifted winding to start, resulting in a characteristic hum.

Question 6: During equipment startup, the compressor short-cycles off on the high-pressure switch after 2 minutes. What should the technician check FIRST?

Suction line insulation integrity
Refrigerant charge level
Thermostat set point
Condenser fan motor operation and airflow restriction (Correct answer)

Correct answer: Condenser fan motor operation and airflow restriction

Condenser fan failure or blocked airflow is the most common cause of high-pressure trips because discharge heat cannot be rejected, causing pressure to spike.

Question 7: 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)
Thermostatic expansion valve (TXV)
Crankcase heater
Low-pressure switch

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 8: What is the purpose of a time-delay fuse in a residential AC disconnect box?

To allow momentary inrush current during compressor startup without blowing (Correct answer)
To prevent nuisance tripping during brownout conditions
To reduce voltage spikes during normal operation
To slow down the circuit breaker response for safety

Correct answer: To allow momentary inrush current during compressor startup without blowing

Time-delay fuses tolerate the high inrush current drawn when the compressor motor starts without opening the circuit.

Question 9: What does 'grains of moisture per pound of dry air' measure in psychrometric terms?

Dew point temperature
Specific humidity or humidity ratio (Correct answer)
Wet-bulb depression
Relative humidity percentage

Correct answer: Specific humidity or humidity ratio

Grains per pound of dry air is the unit for specific humidity (humidity ratio), representing the actual mass of water vapor present per unit of dry air.

Question 10: Nitrogen should be flowing through refrigerant lines during brazing primarily to:

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

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 11: A dual-voltage motor wired for 240V operation will have its internal windings connected in:

Series (Correct answer)
Parallel
Delta configuration
Star configuration

Correct answer: Series

For 240V operation, the windings of a dual-voltage motor are connected in series, while for 120V they are connected in parallel.

Question 12: A residential AC system uses a dual run capacitor. Which terminals are typically labeled on this component?

High, low, and neutral
L1, L2, and ground
C (common), FAN, HERM (Correct answer)
Start, run, and common

Correct answer: C (common), FAN, HERM

A dual run capacitor has three terminals: C (common), HERM (compressor/hermetic), and FAN (condenser fan motor).

Question 13: A technician discovers that a system's operating pressures are within normal range, but the compressor body is abnormally hot. What should be evaluated?

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

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 14: Which fitting produces the least pressure drop when connecting a branch takeoff from a trunk duct?

Conical spin-in fitting
90-degree saddle tap
Wye fitting with a gradual angle (Correct answer)
Straight shoe fitting with a turning vane

Correct answer: Wye fitting with a gradual angle

A wye fitting with a gradual divergence angle smoothly redirects airflow with minimal turbulence, producing the lowest pressure drop of these options.

Question 15: What is the purpose of a static pressure tap in a duct system?

To detect refrigerant leaks in the air handler
To measure air velocity directly
To balance airflow between supply and return
To measure the pressure of air against the duct wall (Correct answer)

Correct answer: To measure the pressure of air against the duct wall

A static pressure tap measures the pressure exerted by air against the duct wall, perpendicular to flow direction.

Question 16: When sizing wire for a residential condensing unit, which document provides the minimum circuit ampacity and maximum overcurrent protection?

Local building department standard tables
Unit installation manual and nameplate data (Correct answer)
NEC Article 210 branch circuit rules only
Manufacturer's suggested retail guidelines

Correct answer: Unit installation manual and nameplate data

The unit nameplate and installation manual list MCA (Minimum Circuit Ampacity) and MOCP (Maximum Overcurrent Protection), which must be used for wire and breaker sizing.

Question 17: 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?

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

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 18: When installing refrigerant line sets in a chase or conduit alongside electrical wiring, the installer must ensure:

Refrigerant lines are wrapped with conductive tape
Both refrigerant and electrical lines share the same conduit to save space
Refrigerant lines are separated from electrical conductors or use NEC-compliant separation methods (Correct answer)
Refrigerant lines are grounded to the electrical conduit

Correct answer: Refrigerant lines are separated from electrical conductors or use NEC-compliant separation methods

The NEC and local codes require separation between refrigerant lines and electrical conductors to prevent insulation damage and potential shock or fire hazards.

Question 19: According to EPA Section 608 regulations, technicians who service systems containing more than 50 lbs of refrigerant must use recovery equipment that meets which standard?

DOT CFR 49 transport standard
ASHRAE 15 safety standard
ARI 740 performance standard (Correct answer)
UL 207 burst pressure standard

Correct answer: ARI 740 performance standard

EPA regulations require that recovery equipment for systems over 50 lbs meet ARI 740 performance efficiency standards.

Question 20: A homeowner reports water dripping from the indoor air handler. The evaporator coil is clear and not frosted. What is the most likely cause?

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

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 21: When installing low-voltage thermostat wire, what is the minimum recommended AWG size for runs up to 100 feet?

12 AWG
18 AWG (Correct answer)
22 AWG
14 AWG

Correct answer: 18 AWG

18 AWG is the industry standard for thermostat wire runs up to approximately 100 feet, providing sufficient conductance to avoid excessive voltage drop in the 24V circuit.

Question 22: What is the safest procedure when connecting manifold gauge hoses to recover refrigerant from a potentially pressurized system?

Attach hoses with valves closed, then slowly open system service valves (Correct answer)
Open the manifold valves first, then attach hoses to prevent pressure lock
Purge all hoses with nitrogen before connecting to the system
Connect the high-side hose last to equalize pressure gradually

Correct answer: Attach hoses with valves closed, then slowly open system service valves

Connecting hoses with manifold valves closed prevents accidental release of refrigerant and controls the rate at which system pressure enters the hoses.

Question 23: A residential condensing unit's condenser fan motor is running but the compressor is not. Which safety device has most likely opened?

Low-pressure switch
Evaporator defrost timer
High-pressure switch or internal thermal overload (Correct answer)
Crankcase heater thermostat

Correct answer: High-pressure switch or internal thermal overload

A high-pressure switch trips when discharge pressure exceeds the set point, or an internal thermal overload opens when the compressor windings overheat, both shutting off the compressor.

Question 24: Designing a residential duct system with excessively high air velocity is generally avoided primarily because it can lead to which of the following issues?

Condensation forming on the outside of the ductwork.
Unacceptable noise levels and increased friction loss. (Correct answer)
Air stratification within the conditioned space.
Reduced heat transfer at the registers.

Correct answer: Unacceptable noise levels and increased friction loss.

When air moves too quickly through ductwork, it creates turbulence which results in undesirable noise (whistling or rushing sounds). High velocity also significantly increases the friction rate (a component of static pressure), which reduces overall airflow and makes the fan work harder.

Question 25: Which document must be completed and left with the homeowner after completing a new residential AC installation?

Local building permit application
Technician's refrigerant purchase receipt
EPA 608 certification copy
Manufacturer's warranty registration and startup checklist (Correct answer)

Correct answer: Manufacturer's warranty registration and startup checklist

Manufacturer warranty registration and the startup checklist must be completed and provided to the homeowner to validate the warranty and document system commissioning.

Question 26: 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)
15 inches Hg vacuum
0 psig

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 27: When charging an R-410A system, the refrigerant cylinder must be kept upright or inverted so that:

Liquid is drawn from the cylinder because R-410A is a near-azeotrope blend (Correct answer)
The pressure gauge reads accurately at all times
Vapor is drawn from the cylinder to avoid liquid slugging the compressor
The desiccant in the cylinder stays active

Correct answer: Liquid is drawn from the cylinder because R-410A is a near-azeotrope blend

R-410A is a near-azeotropic blend that must be charged as a liquid to maintain the correct refrigerant composition ratio.

Question 28: A technician is troubleshooting a system with intermittent cooling. The contactor closes normally but the compressor hums and does not start. What is the most likely cause?

Failed run capacitor (Correct answer)
Defective thermostat
Stuck reversing valve
Open high-pressure switch

Correct answer: Failed run capacitor

A failed or weak run capacitor prevents the compressor from developing enough starting torque, causing it to hum without starting.

Question 29: 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 air filter slot
The electrical wiring terminals
Brazed joints, flare connections, and Schrader valve cores (Correct answer)
The ductwork supply registers

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 30: Which component of the system compresses refrigerant to increase its pressure and temperature?

Compressor (Correct answer)
Evaporator coil
Condenser coil
Expansion valve

Correct answer: Compressor

The compressor is often considered the 'heart' of the air conditioning system. Its primary function is to draw in low-pressure, low-temperature refrigerant vapor from the evaporator and compress it. This compression significantly increases the refrigerant's pressure and temperature, preparing it to release heat in the condenser coil.

Question 31: 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 evaporator coil
Low refrigerant charge
Dirty or blocked condenser coil (Correct answer)
Intermittent thermostat fault

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 32: What is the purpose of installing a crankcase heater on a scroll compressor before startup?

To increase discharge pressure during startup
To prevent high-pressure lockout on cold days
To boil off refrigerant that has migrated into the oil (Correct answer)
To pre-lubricate the compressor bearings

Correct answer: To boil off refrigerant that has migrated into the oil

Crankcase heaters vaporize liquid refrigerant that has migrated into the compressor oil sump, preventing slugging damage on startup.

Question 33: 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?

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

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 34: When installing a split-system condenser, the minimum clearance from the unit to any wall or obstruction on the discharge (top) side should be:

12 inches
6 inches
48 inches
24 inches (Correct answer)

Correct answer: 24 inches

Most manufacturers specify at least 24 inches of clearance above the discharge grille to allow proper airflow and prevent hot air recirculation.

Question 35: A technician uses a clamp meter to measure compressor amperage. The reading is 20% below the rated load amps (RLA). What does this suggest?

The capacitor has failed
The compressor has internal valve leakage reducing workload (Correct answer)
The compressor is healthy and operating efficiently
The system is undercharged with refrigerant

Correct answer: The compressor has internal valve leakage reducing workload

A compressor drawing significantly less than its RLA may indicate worn or leaking internal valves that reduce compression efficiency.

Question 36: When is a mechanical room required by ASHRAE 15 for a residential refrigeration system using a Group A1 refrigerant like R-410A?

Never; Group A1 refrigerants are exempt from mechanical room requirements (Correct answer)
Always, regardless of charge size
Only when the system is installed in a basement
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 37: What does the 'R-value' represent when reading insulation specifications on blueprints?

Thermal resistance of the insulation material (Correct answer)
Roof pitch ratio
Relative humidity rating
Refrigerant charge value

Correct answer: Thermal resistance of the insulation material

R-value measures a material's resistance to heat flow; higher R-values indicate better insulating performance.

Question 38: Which refrigerant is classified as an HFC and is commonly used in residential air conditioning systems manufactured after 2010?

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

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 39: What reading would indicate a shorted run capacitor when tested with a capacitance meter?

Infinite resistance reading
Reading significantly below the rated µF value
Reading slightly above the rated µF value
Reading of 0 µF or OL (overload/short) (Correct answer)

Correct answer: Reading of 0 µF or OL (overload/short)

A shorted capacitor shows 0 µF or an OL symbol on a capacitance meter because the internal dielectric has broken down completely.

Question 40: What is the primary purpose of pressure-testing a refrigerant system with dry nitrogen before adding refrigerant?

To lubricate the compressor before startup
To check system leak integrity without using regulated refrigerant (Correct answer)
To purge moisture from the system
To verify that refrigerant has been fully recovered

Correct answer: To check system leak integrity without using regulated refrigerant

Pressure-testing with dry nitrogen confirms the system is leak-free using a non-regulated, inexpensive gas before introducing environmentally controlled refrigerant.

Question 41: A large wet-bulb depression (big difference between dry-bulb and wet-bulb temperatures) indicates what about the air?

The air is nearly saturated and close to 100% relative humidity
The system refrigerant charge is low and needs recharging
The air is relatively dry with low relative humidity (Correct answer)
The supply air temperature leaving the coil is too high

Correct answer: The air is relatively dry with low relative humidity

A large wet-bulb depression means significant evaporation is occurring from the wet wick, which only happens when the surrounding air has a low relative humidity.

Question 42: What is the Apparatus Dew Point (ADP) of a cooling coil?

The minimum allowable refrigerant temperature within the evaporator
The temperature of condensate water draining from the coil pan
The effective average surface temperature of the coil at which moisture condenses (Correct answer)
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 43: What is the primary function of an evaporator coil in an air conditioning system?

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

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 44: What is subcooling in a refrigeration system?

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

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 45: A crankcase heater on a residential compressor is used primarily for what purpose?

To defrost the outdoor coil during heating mode
To heat the refrigerant before it enters the evaporator
To warm the suction line during low-ambient operation
To prevent refrigerant migration and liquid slugging during the off cycle (Correct answer)

Correct answer: To prevent refrigerant migration and liquid slugging during the off cycle

The crankcase heater keeps the compressor oil warm during the off cycle to prevent refrigerant from migrating into and mixing with the compressor oil, which could cause liquid slugging on startup.

Question 46: Which duct shape provides the most efficient airflow per unit of material used?

Round (Correct answer)
Oval
Rectangular with 2:1 aspect ratio
Square

Correct answer: Round

Round ducts have the lowest surface-area-to-cross-section ratio, minimizing friction losses and material use.

Question 47: What does the term 'locked-rotor amperage' (LRA) mean in the context of an AC compressor?

The current drawn during normal steady-state operation
The minimum current needed to hold the contactor closed
The current drawn when the compressor is fully unloaded
The maximum current drawn at the instant of startup before the motor reaches running speed (Correct answer)

Correct answer: The maximum current drawn at the instant of startup before the motor reaches running speed

LRA is the high inrush current a motor draws at startup when the rotor is stationary, which can be 5–8 times the full-load running amperage.

Question 48: What is the key difference between sensible heat and latent heat in air conditioning?

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

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

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

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 50: While recovering refrigerant, a technician notices that the pressure in the recovery cylinder is rising quickly, slowing down the process. Which of the following is a recommended procedure to manage this issue and speed up recovery?

Increase the heat on the system's liquid line with a torch.
Stop recovery and wait for the pressures to equalize naturally.
Cool the recovery cylinder using a water bath or wet rags. (Correct answer)
Slightly vent the recovery cylinder to relieve pressure.

Correct answer: Cool the recovery cylinder using a water bath or wet rags.

Refrigerant recovery relies on maintaining a pressure differential between the system and the recovery tank. As the tank fills, its internal pressure and temperature rise, slowing recovery. Cooling the cylinder lowers its internal pressure, which helps maintain a favorable pressure difference and speeds up the recovery process.

Question 51: A technician suspects that a system has been contaminated with non-condensables, such as air. Which of the following is the most reliable method to confirm this diagnosis?

Comparing the condenser's saturation temperature (from the gauge) to the ambient temperature after the system has been off for several hours. (Correct answer)
Measuring a very low amp draw on the compressor while the unit is running.
Observing an unusually high superheat reading at the evaporator outlet.
Noticing that the suction line is colder than usual.

Correct answer: Comparing the condenser's saturation temperature (from the gauge) to the ambient temperature after the system has been off for several hours.

After a system has been off long enough for its temperature to equalize with the surrounding air, the pressure inside should correspond to the saturation pressure of the pure refrigerant at that ambient temperature. Non-condensables exert their own partial pressure, resulting in a total system pressure that is higher than the refrigerant's saturation pressure for that ambient temperature. This discrepancy is a definitive sign of contamination.

Question 52: When mounting an air handler in a horizontal position in an attic, which direction should the condensate drain slope?

Downward at exactly 1/2 inch per foot only
Upward toward the unit
Level, with no slope
Downward away from the unit at a minimum 1/8 inch per foot (Correct answer)

Correct answer: Downward away from the unit at a minimum 1/8 inch per foot

Condensate drain lines must slope downward away from the unit at a minimum of 1/8 inch per foot to ensure proper drainage by gravity.

Question 53: When brazing copper refrigerant lines, what minimum silver content is required for the brazing alloy used in most residential AC applications?

5% silver
2% silver
15% silver (Correct answer)
45% 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 54: In a residential AC system, the 'G' terminal on the thermostat controls:

The indoor blower fan relay (Correct answer)
The compressor contactor coil
The reversing valve solenoid
The ground fault protection circuit

Correct answer: The indoor blower fan relay

The G terminal sends a 24V signal to energize the indoor blower fan relay, allowing the fan to run independently for ventilation without calling for cooling or heating.

Question 55: What does SEER stand for and what does it measure?

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

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 56: When pulling a vacuum on a newly installed residential AC system, the system should reach and hold:

Any level below atmospheric pressure
2,000 microns for 10 minutes
5,000 microns for 30 minutes
500 microns or below with no rise above 1,000 microns after isolation (Correct answer)

Correct answer: 500 microns or below with no rise above 1,000 microns after isolation

Industry standard requires the system to reach 500 microns or below; after isolating the vacuum pump, the reading should remain stable and not rise above 1,000 microns, indicating a dry, leak-free system.

Question 57: A technician finds the suction line is sweating heavily all the way back to the compressor. What does this indicate?

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

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

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

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 59: What is the bypass factor of a cooling coil?

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

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 60: When using an oxyacetylene torch for brazing refrigerant lines, the flame should be adjusted to a:

Neutral flame (Correct answer)
Carburizing (reducing) flame
Oxidizing flame
Turbulent blue flame

Correct answer: Neutral flame

A neutral flame provides the correct heat balance for brazing copper without introducing excess oxygen or carbon to the joint.

Question 61: Which type of diagram shows the physical location of components and the actual wire routing between them?

Schematic diagram
Wiring diagram (Correct answer)
Block diagram
Ladder diagram

Correct answer: Wiring diagram

A wiring diagram shows the physical layout and actual routing of wires between components, making it useful for installation and troubleshooting in the field.

Question 62: A technician is lifting a heavy condensing unit. According to OSHA guidelines, when should a mechanical lifting aid be used instead of manual lifting?

Manual lifting is always acceptable if two workers are used
When the load exceeds 50 lbs or safe lifting posture cannot be maintained (Correct answer)
Only when the load exceeds 100 lbs
For any load exceeding 25 lbs

Correct answer: When the load exceeds 50 lbs or safe lifting posture cannot be maintained

OSHA ergonomic guidance recommends mechanical assists for loads over 50 lbs or when proper lifting posture cannot be maintained, reducing musculoskeletal injury risk.

Question 63: How many grains of moisture are in one pound of water?

1,000 grains
10,000 grains
7,000 grains (Correct answer)
5,040 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 64: What does 'EWT' stand for in HVAC load and equipment performance documentation?

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

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

Thermostat (Correct answer)
Contactor
High-pressure switch
Transformer

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 66: R-22 refrigerant recovered from a system and later found to be contaminated must be:

Re-used in any system as long as the refrigerant was recovered legally
Vented to atmosphere since R-22 is being phased out
Reclaimed to AHRI 700 purity standards or sent to a certified reclaimer (Correct answer)
Blended with virgin R-22 before reuse

Correct answer: Reclaimed to AHRI 700 purity standards or sent to a certified reclaimer

Contaminated refrigerant must be reclaimed to AHRI 700 purity standards by an EPA-certified reclaimer before it can be resold or reused in a different system.

Question 67: What causes a compressor to 'short cycle' in a residential air conditioning system?

Oversized system or faulty thermostat causing rapid on/off cycling (Correct answer)
A clogged filter-drier reducing refrigerant flow
High humidity levels causing the coil to absorb too much heat
Undersized ductwork reducing static pressure

Correct answer: Oversized system or faulty thermostat causing rapid on/off cycling

Short cycling typically results from an oversized system that satisfies the thermostat setpoint too quickly or a malfunctioning thermostat, leading to excessive starts and stops.

Question 68: What is the primary difference between refrigerant 'recovery,' 'recycling,' and 'reclaiming'?

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

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 69: When installing a split-system air conditioner, the indoor unit's condensate drain line should be pitched at a minimum slope of:

1 inch per foot
1/4 inch per foot (Correct answer)
1/8 inch per foot
1/2 inch per foot

Correct answer: 1/4 inch per foot

A minimum slope of 1/4 inch per foot ensures proper gravity drainage of condensate without pooling.

Question 70: Why is grounding important in air conditioning electrical systems?

To provide a safe path for electrical faults (Correct answer)
To increase motor efficiency
To stabilize voltage fluctuations
To reduce energy consumption

Correct answer: To provide a safe path for electrical faults

Grounding is a critical safety measure in electrical systems, including air conditioning units. It provides a low-resistance path for fault currents to safely dissipate into the earth, preventing dangerous electrical shocks to occupants and protecting equipment from damage in case of a short circuit or insulation failure.

Question 71: What does a dashed line typically represent on a mechanical floor plan?

Structural beams
Hidden or overhead ductwork (Correct answer)
Plumbing drain lines
Electrical conduit

Correct answer: Hidden or overhead ductwork

Dashed lines on mechanical plans typically indicate ducts or components located above or below the primary plane of view.

Question 72: What does the 'W' terminal on a residential thermostat control?

Cooling (compressor) circuit
Fan-only operation
Humidifier or dehumidifier circuit
Heating (furnace or heat pump) circuit (Correct answer)

Correct answer: Heating (furnace or heat pump) circuit

The W terminal carries the heat call signal, energizing the furnace burner, electric heat strips, or heat pump reversing valve depending on the system type.

Question 73: When installing ductwork for a new residential AC system, what is the purpose of using mastic sealant instead of standard duct tape?

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

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 74: A residential AC system trips the breaker repeatedly after running for 10–15 minutes. The MOST likely electrical cause is:

A faulty thermostat R wire connection
Compressor drawing excessive amperage due to a failing motor or refrigerant overcharge (Correct answer)
Corroded thermostat heat anticipator
A weak 24V control transformer

Correct answer: Compressor drawing excessive amperage due to a failing motor or refrigerant overcharge

Thermal trip after a short run time typically indicates the compressor is drawing above-normal current, which could be caused by a failing motor winding or an overcharged refrigerant system.

Question 75: What is the typical temperature differential (TD) across a properly functioning residential evaporator coil?

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

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 76: Which electrical test would BEST confirm that a compressor motor winding has a ground fault?

Measure current draw with a clamp meter during startup
Measure resistance between each winding terminal and the compressor shell/ground (Correct answer)
Measure resistance between the two run terminals
Measure voltage across the run capacitor terminals

Correct answer: Measure resistance between each winding terminal and the compressor shell/ground

A megohmmeter or ohmmeter reading between a winding terminal and the grounded shell detects insulation breakdown indicating a ground fault.

Question 77: In a residential air conditioning system, the low-voltage thermostat wire labeled 'Y' is used to signal:

Emergency heat activation
Cooling demand to energize the compressor contactor (Correct answer)
Humidifier operation
Fan-only operation

Correct answer: Cooling demand to energize the compressor contactor

The Y wire carries the cooling call signal from the thermostat to the air handler or furnace control board, which then energizes the outdoor unit contactor.

Question 78: During installation, which type of pipe insulation is most suitable for residential refrigerant suction lines?

Open-cell foam insulation
Closed-cell foam insulation (Correct answer)
Rubber pipe wrap tape
Fiberglass wrap

Correct answer: Closed-cell foam insulation

Closed-cell foam insulation is preferred for suction lines because it resists moisture absorption and provides effective thermal insulation.

Question 79: Which duct leakage test measures total system leakage including leakage to conditioned space?

Leakage to outside test
Duct blaster total leakage test (Correct answer)
Pressure pan test
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 80: What is the primary difference between a single-stage and a two-stage compressor in residential AC?

Two-stage operates at full and partial capacity; single-stage runs at full capacity only (Correct answer)
Two-stage requires twice the refrigerant charge of a single-stage unit
Single-stage has two cylinders; two-stage has one variable-speed cylinder
Two-stage uses two refrigerant circuits; single-stage uses one

Correct answer: Two-stage operates at full and partial capacity; single-stage runs at full capacity only

A two-stage compressor can run at a lower capacity stage during mild conditions and switch to full capacity during peak demand, improving efficiency and comfort.

Question 81: During refrigerant recovery, what does a rising pressure on the recovery machine's discharge gauge while the suction side is in deep vacuum most likely indicate?

Non-condensable gases (air) are present in the recovered refrigerant (Correct answer)
The system expansion valve is restricting refrigerant flow
The recovery machine compressor is overheating
The recovery cylinder is nearly full

Correct answer: Non-condensable gases (air) are present in the recovered refrigerant

Non-condensable gases like air do not condense at normal recovery temperatures, causing discharge pressure to rise even after the suction side reaches deep vacuum.

Question 82: Which document must a refrigerant reclaimation facility provide to verify that recovered refrigerant meets AHRI 700 purity standards?

Certificate of Reclaim (analysis report) (Correct answer)
DOT Form HM-181
EPA Form 7630
Manufacturer's Safety Data Sheet (SDS)

Correct answer: Certificate of Reclaim (analysis report)

A certified reclaimer issues a certificate of reclaim (or analysis report) confirming the refrigerant meets AHRI Standard 700 purity requirements.

Question 83: When using an electronic leak detector and no leak is found at suspected areas, what technique should the technician use next?

Increase system pressure by adding refrigerant
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

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 84: The primary purpose of installing a filter-drier in the liquid line of a new residential AC system is to:

Reduce refrigerant velocity before the metering device
Increase subcooling of the liquid refrigerant
Remove moisture and contaminants that could damage the system (Correct answer)
Measure refrigerant flow rate

Correct answer: Remove moisture and contaminants that could damage the system

A filter-drier absorbs moisture and traps particulates, protecting the metering device and compressor from contamination and acid formation.

Question 85: What happens to airflow velocity when a duct transitions from a smaller to a larger cross-section?

Velocity decreases and static pressure partially recovers (Correct answer)
Velocity doubles and static pressure drops proportionally
Velocity increases due to the pressure buildup
Velocity stays the same but turbulence increases

Correct answer: Velocity decreases and static pressure partially recovers

When a duct expands, the air slows down (by continuity) and some velocity pressure converts back to static pressure—this is called static regain.

Question 86: Which of the following is a critical safety practice that must be followed when brazing refrigerant lines in an enclosed space?

Wearing standard sunglasses to protect from the bright flame.
Ensuring the area is well-ventilated to prevent the accumulation of harmful fumes. (Correct answer)
Having a pressurized water extinguisher ready at all times.
Keeping the nitrogen purge pressure above 20 PSI to speed up the process.

Correct answer: Ensuring the area is well-ventilated to prevent the accumulation of harmful fumes.

Brazing produces fumes from the flux, base metals, and filler metals, which can be hazardous if inhaled, especially in confined areas. Proper ventilation, such as using an exhaust fan, is essential to remove these fumes and maintain a safe breathing environment. Personal Protective Equipment (PPE) like proper shaded goggles and heat-resistant gloves are also crucial.

Question 87: What is the primary function of a humidistat in a residential HVAC system?

To measure refrigerant pressure on the suction line
To measure the temperature differential across the evaporator coil
To sense indoor relative humidity and signal the system to humidify or dehumidify (Correct answer)
To regulate blower motor speed based on duct static pressure

Correct answer: To sense indoor relative humidity and signal the system to humidify or dehumidify

A humidistat detects relative humidity and cycles humidification or dehumidification equipment to maintain the set humidity level, functioning like a thermostat but for moisture.

Question 88: In modern, high-efficiency residential air handlers, which type of motor is commonly used to provide variable airflow and improve system efficiency?

Capacitor-start induction-run motor
Permanent Split Capacitor (PSC) motor
Electronically Commutated Motor (ECM) (Correct answer)
Shaded-pole 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 89: What is the purpose of the reversing valve in a heat pump system?

To prevent refrigerant from flowing back through the compressor
To regulate refrigerant flow based on outdoor temperature
To equalize high and low side pressures during shutdown
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 90: What happens to the boiling point of a refrigerant when pressure increases?

The boiling point decreases
The refrigerant solidifies
The boiling point increases (Correct answer)
The boiling point stays the same

Correct answer: The boiling point increases

Higher pressure raises the saturation (boiling) temperature of a refrigerant, which is why condenser pressures are higher than evaporator pressures.

Question 91: In a residential AC ladder diagram, each horizontal 'rung' of the ladder represents:

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

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 92: Which principle explains the heat absorption in the evaporator coil?

Adiabatic cooling
Latent heat transfer during phase change (Correct answer)
Thermal conduction
Sensible heat transfer

Correct answer: Latent heat transfer during phase change

The evaporator coil cools the air primarily through latent heat transfer. As the liquid refrigerant inside the coil absorbs heat from the indoor air, it changes phase from a liquid to a gas (vaporizes) without a significant change in its own temperature. This phase change efficiently removes a large amount of heat from the surrounding air.

Question 93: What does a megohmmeter (megger) test on a compressor motor measure?

Insulation resistance between windings and ground (Correct answer)
Capacitor microfarad rating
Supply voltage quality
Winding resistance in ohms

Correct answer: Insulation resistance between windings and ground

A megohmmeter applies high DC voltage to measure insulation resistance, revealing moisture or degradation in motor windings.

Question 94: What does the Sensible Heat Ratio (SHR) of a cooling system represent?

The ratio of supply air temperature to return air temperature
The ratio of latent heat removal to total heat removal
The ratio of indoor humidity to outdoor humidity
The ratio of sensible heat removal to total heat removal (sensible plus latent) (Correct answer)

Correct answer: The ratio of sensible heat removal to total heat removal (sensible plus latent)

SHR = sensible load ÷ (sensible load + latent load), indicating what fraction of total cooling capacity handles temperature reduction versus dehumidification.

Question 95: What is the recommended maximum air velocity in a main supply trunk duct for a low-noise residential HVAC system?

900 FPM (Correct answer)
1500 FPM
600 FPM
1200 FPM

Correct answer: 900 FPM

Main trunk ducts in residential systems are typically designed for 900 FPM to balance noise and efficiency.

Question 96: Which insulation vapor barrier placement is correct for a duct located in a hot, humid unconditioned attic?

Vapor barrier on the outside of the insulation facing the attic (Correct answer)
No vapor barrier is needed in attic installations
Vapor barrier only on the return duct
Vapor barrier on the inside of the duct liner

Correct answer: Vapor barrier on the outside of the insulation facing the attic

In a hot-humid attic, the vapor barrier must face outward to block moisture from the warm attic air from reaching the cold duct surface.

Question 97: What does a high latent load in a residential building indicate?

The building envelope has insufficient insulation for the climate
The ductwork is undersized and restricting airflow
There is significant moisture that the cooling system must condense and remove (Correct answer)
The supply air temperature must be lowered to maintain comfort

Correct answer: There is significant moisture that the cooling system must condense and remove

A high latent load means large amounts of moisture — from occupants, infiltration, cooking, or plants — are entering the space and must be removed by the AC system.

Question 98: 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, superheated vapor
High-pressure, high-temperature vapor
Low-pressure, low-temperature liquid
High-pressure, warm liquid (Correct answer)

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 99: Which condition would MOST likely cause a recovery machine to short-cycle (start and stop rapidly) during vapor-phase recovery?

An oversized recovery cylinder creating too much pressure differential
Refrigerant oil contaminating the recovery machine's suction port
A refrigerant system with very low remaining charge and near-vacuum pressures (Correct answer)
High ambient temperature reducing condenser efficiency

Correct answer: A refrigerant system with very low remaining charge and near-vacuum pressures

When system pressure drops near vacuum as the charge is depleted, the recovery machine's low-pressure cutout trips repeatedly, causing short-cycling.

Question 100: A residential split system has the evaporator coil located in the:

Condensate drain pan only
Outdoor condenser cabinet
Compressor compartment
Indoor air handler or furnace plenum (Correct answer)

Correct answer: Indoor air handler or furnace plenum

In a split system, the evaporator coil is installed indoors in the air handler or above the furnace to cool circulating air.

Question 101: In troubleshooting with a schematic, if voltage is present on both sides of a normally closed safety switch, what does this indicate?

The switch is functioning normally and the circuit is complete
The switch is bypassed by a parallel circuit
The switch has opened (tripped) and is blocking current flow to the load (Correct answer)
The switch is welded closed and cannot open

Correct answer: The switch has opened (tripped) and is blocking current flow to the load

Voltage on both sides of an open switch (with load connected) indicates the switch contacts are open — voltage is present at the input but cannot pass through to the output.

Question 102: During a maintenance visit, a technician finds the evaporator coil heavily coated with mold and biological growth. What is the recommended maintenance procedure?

Clean the coil with an EPA-registered coil cleaner and treat with an antimicrobial solution (Correct answer)
Spray the coil with bleach and rinse with a garden hose
Run the system at maximum cooling to freeze off the growth
Replace the entire air handler immediately

Correct answer: Clean the coil with an EPA-registered coil cleaner and treat with an antimicrobial solution

Evaporator coils with mold growth should be cleaned with an EPA-registered coil cleaner and treated with an approved antimicrobial solution to eliminate biological contamination safely.

Question 103: When reviewing a set of mechanical blueprints for a new residential installation, where should a technician first look to understand what a specific symbol, such as a square with an 'X' inside, represents?

The architectural floor plan
The equipment schedule
The general notes section
The legend or symbol list (Correct answer)

Correct answer: The legend or symbol list

The legend or symbol list on a blueprint serves as a dictionary, defining every symbol, icon, and line type used in the drawings. While other sections provide important information, the legend is the primary reference for identifying components like a supply air diffuser (often shown as a square with an 'X').

Question 104: Which type of metering device maintains a constant evaporator outlet superheat regardless of load changes?

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

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.

Question 105: What are the primary negative effects of high indoor relative humidity on occupants?

It improves air quality by causing airborne dust particles to clump and settle
It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation (Correct answer)
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 106: During system-dependent (passive) recovery, refrigerant is transferred using:

Gravity flow from a higher-pressure liquid line
An external recovery machine compressor
A vacuum pump connected to the low side
The system's own compressor to push refrigerant into recovery cylinders (Correct answer)

Correct answer: The system's own compressor to push refrigerant into recovery cylinders

System-dependent recovery uses the appliance's own compressor to pump refrigerant into recovery cylinders without an external machine.

Question 107: What is the primary reason duct leakage in an attic is more detrimental than duct leakage in a conditioned basement?

Attic ducts are always larger and lose more air
Leakage into unconditioned attic space is a complete energy loss, while basement leakage stays within the thermal envelope (Correct answer)
Basement duct leaks cause condensation on walls
Attic leaks violate local codes while basement leaks do not

Correct answer: Leakage into unconditioned attic space is a complete energy loss, while basement leakage stays within the thermal envelope

Air leaking into an unconditioned attic is permanently lost from the system, whereas leakage into a conditioned basement still benefits the space.

Question 108: What is the purpose of a time-delay relay (TDR) in an AC system schematic?

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

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

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

Correct answer: Balancing collar

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

Question 110: What does the symbol for a fuse look like on a standard electrical schematic?

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

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 111: A technician measures suction pressure significantly above normal and discharge pressure below normal on a residential split system. What is the most likely cause?

Low refrigerant charge
Restricted liquid line filter-drier
Compressor valve failure (Correct answer)
Refrigerant overcharge

Correct answer: Compressor valve failure

Compressor valve failure causes high suction and low discharge pressure because refrigerant bypasses the compressor valves instead of being properly compressed.

Question 112: When checking for a refrigerant non-condensable gas contamination, what symptom would be most evident?

Low suction pressure and normal head pressure
High head pressure that does not correspond to expected saturation temperature (Correct answer)
Very low subcooling with normal superheat
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 113: Which of the following best describes 'swaging' in refrigerant line work?

Cutting a tube at a precise angle for flared connections
Expanding the end of a tube so another tube of the same diameter can be inserted for brazing (Correct answer)
Removing burrs from a cut tube end
Bending tubing without kinking

Correct answer: Expanding the end of a tube so another tube of the same diameter can be inserted for brazing

Swaging expands the end of one tube to accept another tube of the same diameter, creating a socket joint suitable for brazing.

Question 114: When refrigerant is recovered from a system and later sent to a reclaimer, the reclaimer is required by EPA to:

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

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 115: According to EPA regulations, technicians must keep records of refrigerant recovery for commercial appliances containing more than how many pounds of refrigerant?

20 pounds (Correct answer)
15 pounds
5 pounds
50 pounds

Correct answer: 20 pounds

EPA Section 608 requires that service records be kept for appliances containing more than 20 pounds of refrigerant, documenting the amount recovered and disposed of.

Question 116: A run capacitor rated 45+5 MFD is used with a condenser fan motor and compressor. What do the two capacitance values represent?

Primary and secondary winding values
Startup and shutdown capacitance
Compressor and fan motor capacitance respectively (Correct answer)
Capacitance at high and low ambient temperatures

Correct answer: Compressor and fan motor capacitance respectively

In a dual-run capacitor, the larger value (45 MFD) serves the compressor and the smaller value (5 MFD) serves the condenser fan motor.

Question 117: When measuring amperage on a dual-voltage (208/240V) compressor operating at 240V, the current draw is 18A. What would you expect if the same compressor runs at 208V?

Higher amperage (Correct answer)
Same amperage
Lower amperage
The compressor cannot run at 208V

Correct answer: Higher amperage

At lower voltage with the same load, current must increase to deliver equivalent power (P = V × I).

Question 118: In a vapor-compression cycle, which component raises refrigerant pressure and temperature?

Compressor (Correct answer)
Filter-drier
Evaporator
Thermostatic expansion valve

Correct answer: Compressor

The compressor draws in low-pressure vapor and raises it to high pressure and temperature before sending it to the condenser.

Question 119: What duct material is NOT recommended for use in return air systems because it can off-gas harmful compounds when exposed to the airstream?

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

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 120: When replacing a TXV, the technician must ensure the sensing bulb is:

Submerged in the condensate drain pan
Clamped firmly to the suction line and insulated from ambient air (Correct answer)
Installed on the discharge line near the compressor
Positioned inside the return air duct

Correct answer: Clamped firmly to the suction line and insulated from ambient air

The TXV sensing bulb must make good thermal contact with the suction line and be insulated so it accurately senses refrigerant vapor temperature, not ambient temperature.

Question 121: 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 122: What is the correct procedure for sealing a connection between a flexible duct collar and a sheet metal fitting?

Use duct tape rated for duct use (UL 181B-FX) and pull the outer jacket over the collar (Correct answer)
Use zip ties only; tape is not code-compliant
Apply spray foam insulation around the collar and cover with foil tape
Self-tapping screws alone are sufficient

Correct answer: Use duct tape rated for duct use (UL 181B-FX) and pull the outer jacket over the collar

UL 181B-FX tape must be used to seal the inner liner to the collar, and the outer jacket and insulation should then be pulled over and secured with a tie or clamp.

Question 123: On a residential AC system, what is the role of the low-voltage common wire (C-wire) connected to the thermostat?

To send the cooling call signal to the contactor
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 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 124: 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?

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

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

The analysis of duct static pressure losses
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)

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

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

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

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

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 128: During system startup, the technician measures suction pressure lower than expected and superheat higher than normal. What is the most likely cause?

Excessive airflow across the evaporator
Overcharge of refrigerant
Restricted liquid line filter-drier (Correct answer)
Oversized metering device

Correct answer: Restricted liquid line filter-drier

A restricted liquid line filter-drier causes a pressure drop that starves the metering device, resulting in low suction pressure and high superheat.

Question 129: 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?

56.1 lbs (Correct answer)
38.1 lbs
47.6 lbs
65.6 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 130: On a psychrometric chart, wet-bulb temperature lines run in which direction?

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

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 131: What refrigerant container color indicates R-410A under the ARI (now AHRI) color-coding standard?

Light blue (sky blue)
Medium purple (rose)
Orange
Pink (rose) (Correct answer)

Correct answer: Pink (rose)

ARI/AHRI standard color coding assigns rose/pink to R-410A cylinders, helping technicians quickly identify refrigerant type.

Question 132: What is the function of a filter-drier in a refrigerant circuit?

Remove moisture and contaminants from the refrigerant (Correct answer)
Measure system superheat
Regulate refrigerant flow to the evaporator
Sense outdoor ambient temperature

Correct answer: Remove moisture and contaminants from the refrigerant

The filter-drier contains desiccant material that absorbs moisture and captures particulates to protect system components.

Question 133: A technician is inspecting ductwork in an attic and identifies a type of duct constructed with a helical wire coil core, covered by a polymer plastic liner, a layer of insulation, and an outer vapor barrier jacket. Which type of duct material is this?

Fiberglass duct board
Flexible duct (Flex duct) (Correct answer)
Sheet metal duct
PVC duct

Correct answer: Flexible duct (Flex duct)

This description accurately portrays the construction of a flexible duct, often called 'flex duct'. It consists of a spring-like wire coil that forms the tube, an inner plastic liner, a layer of fiberglass insulation, and a protective outer jacket, which is often foil or polyethylene.

Question 134: What is the purpose of the time-delay relay (TDR) found in some residential AC control circuits?

Prevents compressor short-cycling by enforcing a minimum off time between starts (Correct answer)
Delays thermostat response to prevent rapid temperature swings
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 135: What happens to a run capacitor's capacitance value as it ages and begins to fail?

It remains stable but its voltage rating drops
It fluctuates randomly between high and low values
It increases above its rated MFD
It decreases below its rated MFD (Correct answer)

Correct answer: It decreases below its rated MFD

As a run capacitor ages, its dielectric deteriorates and capacitance decreases, reducing its ability to maintain motor efficiency and causing overheating.

Question 136: 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 137: A residential AC system is running, and the compressor is functioning correctly. What is the expected state of the refrigerant as it enters the compressor?

Low-pressure, superheated vapor (Correct answer)
High-pressure, saturated liquid/vapor mix
High-pressure, superheated vapor
Low-pressure, subcooled liquid

Correct answer: Low-pressure, superheated vapor

The refrigerant leaves the evaporator as a low-pressure vapor. It should be slightly superheated, meaning its temperature is above its boiling point, to ensure no liquid refrigerant enters and damages the compressor.

Question 138: A technician measures a compressor drawing high amperage with low suction and high discharge pressure. What is the most likely diagnosis?

Refrigerant undercharge
Refrigerant overcharge (Correct answer)
Liquid slugging
Failed condenser fan motor

Correct answer: Refrigerant overcharge

Refrigerant overcharge increases system pressures and compressor workload, resulting in elevated amperage draw.

Question 139: 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 regulate refrigerant pressure during startup
To provide surge protection during lightning storms
To boost starting torque and reduce locked-rotor amperage duration (Correct answer)

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 140: Which of the following documents is essential for determining the correct equipment size and capacity for a new residential air conditioning installation?

A Manual J load calculation report. (Correct answer)
The manufacturer's warranty registration form.
The local building permit application.
The homeowner's previous utility bills.

Correct answer: A Manual J load calculation report.

A Manual J load calculation is the industry standard method for determining the precise heating and cooling needs of a specific house. It accounts for factors like square footage, insulation levels, window type and orientation, air leakage, and local climate data. Sizing a system based on this calculation ensures optimal performance, efficiency, and comfort, preventing issues like short-cycling or inadequate dehumidification.

Question 141: 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?

0.30 in. w.g.
0.18 in. w.g. (Correct answer)
0.22 in. w.g.
0.13 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 142: What is relative humidity (RH)?

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

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

Control the flow of outdoor air
Condense the refrigerant
Reduce refrigerant pressure and temperature (Correct answer)
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 144: Which refrigerant cycle process occurs in the condenser?

Heat absorption from indoor air
Condensation and heat rejection to outdoor air (Correct answer)
Evaporation at low pressure
Pressure reduction through a fixed orifice

Correct answer: Condensation and heat rejection to outdoor air

In the condenser, high-pressure refrigerant vapor releases heat to the outside air and condenses into a liquid.

Question 145: Under what condition does condensation form on interior window surfaces?

When the window surface temperature drops below the dew point of the indoor air (Correct answer)
Whenever indoor relative humidity exceeds 30%
Only when outdoor temperatures exceed indoor temperatures
Whenever indoor relative humidity exceeds 50%

Correct answer: When the window surface temperature drops below the dew point of the indoor air

Condensation forms on any surface whose temperature falls below the dew point of the surrounding air, regardless of a single fixed RH percentage.

Question 146: When transferring liquid refrigerant from a recovery cylinder to a system, the technician should:

Use the recovery machine in reverse to push liquid under pressure
Connect the cylinder vapor port to the system high side
Invert the cylinder or use the liquid valve to push liquid into the low side (Correct answer)
Connect the cylinder liquid port to the system low side with the cylinder upright

Correct answer: Invert the cylinder or use the liquid valve to push liquid into the low side

Inverting the cylinder or using the dip-tube liquid valve ensures liquid refrigerant flows out; connecting to the high side helps push the charge into the system.

Question 147: What does the ASHRAE Standard 15 primarily govern in HVAC applications?

Refrigerant leak detection alarm thresholds only
Energy efficiency ratings for air conditioners
Indoor air quality ventilation rates
Safety code for mechanical refrigeration systems (Correct answer)

Correct answer: Safety code for mechanical refrigeration systems

ASHRAE Standard 15 is the Safety Standard for Refrigeration Systems, covering safe design, construction, installation, and operation of refrigerating systems.

Question 148: Which of the following refrigerants is classified as an A2L (mildly flammable) refrigerant?

R-32 (Correct answer)
R-22
R-134a
R-410A

Correct answer: R-32

R-32 is classified A2L — lower flammability limit above 3.5% by volume and a burning velocity ≤10 cm/s — unlike the A1 refrigerants R-22 and R-410A.

Question 149: A rectangular duct measures 12 inches by 8 inches. What is its equivalent round duct diameter?

9.6 inches (Correct answer)
8.8 inches
11.3 inches
10.7 inches

Correct answer: 9.6 inches

The equivalent diameter for a 12×8 rectangular duct using the hydraulic diameter formula is approximately 9.6 inches.

Question 150: In load calculations, what does 'sensible heat' refer to?

Heat transferred by radiation from the sun
Heat that changes the moisture content of air
Total heat content of air including moisture
Heat that changes air temperature without changing moisture content (Correct answer)

Correct answer: Heat that changes air temperature without changing moisture content

Sensible heat causes a measurable temperature change in the air without altering its moisture (humidity) content.

Question 151: 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?

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

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 152: The suction line in a residential split system is typically insulated to:

Prevent condensation and maintain superheat entering the compressor (Correct answer)
Prevent refrigerant from overheating
Reduce refrigerant velocity
Lower the discharge pressure

Correct answer: Prevent condensation and maintain superheat entering the compressor

Insulating the suction line prevents heat gain from the ambient air, which could cause excessive superheat and reduce system efficiency.

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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