DC HVAC Master Mechanic Exam
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. Which refrigerant system component is primarily responsible for
reducing high-pressure liquid refrigerant into a low-pressure mixture
before it enters the evaporator?
A. Compressor
B. Condenser
C. Expansion valve
D. Receiver
Correct Answer: C. Expansion valve
The expansion valve controls refrigerant flow and creates a pressure drop
that allows the refrigerant to absorb heat in the evaporator.
2. In a vapor-compression HVAC system, the compressor’s main function
is to:
A. Remove moisture from refrigerant
B. Increase refrigerant pressure and temperature
C. Reduce refrigerant temperature
D. Separate oil from refrigerant
,Correct Answer: B. Increase refrigerant pressure and temperature
The compressor compresses low-pressure vapor refrigerant into high-
pressure vapor, preparing it for heat rejection in the condenser.
3. According to standard HVAC electrical practices, the purpose of a
contactor in an air-conditioning unit is to:
A. Measure refrigerant pressure
B. Control refrigerant temperature
C. Switch high-voltage loads using a low-voltage signal
D. Increase motor speed
Correct Answer: C. Switch high-voltage loads using a low-voltage signal
A contactor uses a low-voltage control circuit to energize and disconnect
high-voltage components such as compressors and condenser fan motors.
4. A superheat measurement in an evaporator system represents:
A. The temperature of liquid refrigerant leaving the condenser
B. The temperature increase of vapor refrigerant above its boiling point
C. The pressure difference across the compressor
D. The amount of oil in the compressor
Correct Answer: B. The temperature increase of vapor refrigerant above its
boiling point
Superheat indicates how much the refrigerant vapor temperature exceeds
its saturation temperature and helps prevent liquid refrigerant from
entering the compressor.
5. What instrument is used to measure refrigerant pressure in HVAC
systems?
A. Multimeter
B. Manifold gauge set
,C. Clamp meter
D. Hygrometer
Correct Answer: B. Manifold gauge set
A manifold gauge set measures suction and discharge pressures and assists
technicians in diagnosing refrigeration system operation.
6. The primary purpose of a condenser coil is to:
A. Absorb heat from indoor air
B. Reject heat from refrigerant to the surrounding environment
C. Increase refrigerant pressure
D. Remove oil from the compressor
Correct Answer: B. Reject heat from refrigerant to the surrounding
environment
The condenser releases heat absorbed from the conditioned space and
converts refrigerant vapor into liquid.
7. In an HVAC system, a dirty air filter commonly causes:
A. Increased airflow
B. Reduced system efficiency and airflow restriction
C. Higher refrigerant charge
D. Increased compressor lubrication
Correct Answer: B. Reduced system efficiency and airflow restriction
A clogged filter restricts airflow, reducing heat transfer and forcing the
system to operate inefficiently.
8. A master HVAC mechanic should verify refrigerant recovery equipment
is used because:
A. Refrigerant can be safely vented outdoors
B. Refrigerants must be recovered to prevent environmental harm
, C. Recovery increases compressor speed
D. Recovery eliminates the need for leak testing
Correct Answer: B. Refrigerants must be recovered to prevent
environmental harm
Environmental regulations require proper refrigerant recovery instead of
releasing refrigerants into the atmosphere.
9. The evaporator coil in an air-conditioning system:
A. Rejects heat outdoors
B. Absorbs heat from indoor air
C. Compresses refrigerant
D. Stores refrigerant oil
Correct Answer: B. Absorbs heat from indoor air
The evaporator absorbs heat as refrigerant changes from liquid to vapor
inside the coil.
10. What is the purpose of a crankcase heater on a compressor?
A. Increase refrigerant pressure
B. Prevent refrigerant migration into compressor oil during shutdown
C. Cool the compressor motor
D. Increase airflow
Correct Answer: B. Prevent refrigerant migration into compressor oil during
shutdown
A crankcase heater keeps refrigerant from mixing with compressor oil,
reducing startup damage.
11. A low-pressure switch in an HVAC system is designed to:
A. Protect against loss of refrigerant charge
B. Increase condenser pressure
Practice Questions And Correct Answers
(Verified Answers) Plus Rationale 2026
Q&A| Instant Download Pdf
1. Which refrigerant system component is primarily responsible for
reducing high-pressure liquid refrigerant into a low-pressure mixture
before it enters the evaporator?
A. Compressor
B. Condenser
C. Expansion valve
D. Receiver
Correct Answer: C. Expansion valve
The expansion valve controls refrigerant flow and creates a pressure drop
that allows the refrigerant to absorb heat in the evaporator.
2. In a vapor-compression HVAC system, the compressor’s main function
is to:
A. Remove moisture from refrigerant
B. Increase refrigerant pressure and temperature
C. Reduce refrigerant temperature
D. Separate oil from refrigerant
,Correct Answer: B. Increase refrigerant pressure and temperature
The compressor compresses low-pressure vapor refrigerant into high-
pressure vapor, preparing it for heat rejection in the condenser.
3. According to standard HVAC electrical practices, the purpose of a
contactor in an air-conditioning unit is to:
A. Measure refrigerant pressure
B. Control refrigerant temperature
C. Switch high-voltage loads using a low-voltage signal
D. Increase motor speed
Correct Answer: C. Switch high-voltage loads using a low-voltage signal
A contactor uses a low-voltage control circuit to energize and disconnect
high-voltage components such as compressors and condenser fan motors.
4. A superheat measurement in an evaporator system represents:
A. The temperature of liquid refrigerant leaving the condenser
B. The temperature increase of vapor refrigerant above its boiling point
C. The pressure difference across the compressor
D. The amount of oil in the compressor
Correct Answer: B. The temperature increase of vapor refrigerant above its
boiling point
Superheat indicates how much the refrigerant vapor temperature exceeds
its saturation temperature and helps prevent liquid refrigerant from
entering the compressor.
5. What instrument is used to measure refrigerant pressure in HVAC
systems?
A. Multimeter
B. Manifold gauge set
,C. Clamp meter
D. Hygrometer
Correct Answer: B. Manifold gauge set
A manifold gauge set measures suction and discharge pressures and assists
technicians in diagnosing refrigeration system operation.
6. The primary purpose of a condenser coil is to:
A. Absorb heat from indoor air
B. Reject heat from refrigerant to the surrounding environment
C. Increase refrigerant pressure
D. Remove oil from the compressor
Correct Answer: B. Reject heat from refrigerant to the surrounding
environment
The condenser releases heat absorbed from the conditioned space and
converts refrigerant vapor into liquid.
7. In an HVAC system, a dirty air filter commonly causes:
A. Increased airflow
B. Reduced system efficiency and airflow restriction
C. Higher refrigerant charge
D. Increased compressor lubrication
Correct Answer: B. Reduced system efficiency and airflow restriction
A clogged filter restricts airflow, reducing heat transfer and forcing the
system to operate inefficiently.
8. A master HVAC mechanic should verify refrigerant recovery equipment
is used because:
A. Refrigerant can be safely vented outdoors
B. Refrigerants must be recovered to prevent environmental harm
, C. Recovery increases compressor speed
D. Recovery eliminates the need for leak testing
Correct Answer: B. Refrigerants must be recovered to prevent
environmental harm
Environmental regulations require proper refrigerant recovery instead of
releasing refrigerants into the atmosphere.
9. The evaporator coil in an air-conditioning system:
A. Rejects heat outdoors
B. Absorbs heat from indoor air
C. Compresses refrigerant
D. Stores refrigerant oil
Correct Answer: B. Absorbs heat from indoor air
The evaporator absorbs heat as refrigerant changes from liquid to vapor
inside the coil.
10. What is the purpose of a crankcase heater on a compressor?
A. Increase refrigerant pressure
B. Prevent refrigerant migration into compressor oil during shutdown
C. Cool the compressor motor
D. Increase airflow
Correct Answer: B. Prevent refrigerant migration into compressor oil during
shutdown
A crankcase heater keeps refrigerant from mixing with compressor oil,
reducing startup damage.
11. A low-pressure switch in an HVAC system is designed to:
A. Protect against loss of refrigerant charge
B. Increase condenser pressure
