AZ L-39 Air Conditioning & Refrigeration
Contractor Exam Questions and Correct
Answers (Verified Answers) Plus Rationale
2027 Q&A| Instant Download Pdf
1. What is the primary function of an evaporator in a vapor-
compression refrigeration system?
a. To reject heat from the refrigerant to the outdoor air
b. To increase the refrigerant pressure
c. To absorb heat from the space or material being cooled
d. To remove moisture from the compressor oil
Rationale: The evaporator absorbs heat from the conditioned space as
low-pressure refrigerant evaporates inside its coils. This heat
absorption produces the cooling effect. The condenser performs the
opposite function by rejecting heat to the surroundings.
,2. What is the primary purpose of a compressor in a refrigeration
system?
a. To reduce refrigerant pressure below atmospheric pressure
b. To remove moisture from the refrigerant
c. To compress refrigerant vapor, increasing its pressure and
temperature
d. To convert high-pressure liquid refrigerant into low-pressure liquid
Rationale: The compressor draws low-pressure refrigerant vapor from
the evaporator and compresses it into high-pressure, high-
temperature vapor. This allows the refrigerant to release heat in the
condenser and continue circulating through the system.
3. Which component removes heat from high-pressure refrigerant
vapor and converts it into liquid?
a. Evaporator
b. Expansion valve
c. Accumulator
d. Condenser
,Rationale: The condenser transfers heat from the refrigerant to
outdoor air or cooling water. As the refrigerant loses heat, it
condenses from vapor into liquid at approximately constant pressure.
4. What is the primary function of a thermostatic expansion valve
(TXV)?
a. To maintain a constant compressor discharge temperature
b. To regulate condenser fan speed
c. To control refrigerant flow into the evaporator in response to
superheat
d. To prevent refrigerant from entering the condenser
Rationale: A TXV regulates refrigerant flow based on evaporator
outlet superheat. It helps maintain effective evaporator utilization
while preventing excessive liquid refrigerant from returning to the
compressor.
5. What does superheat represent in a refrigeration system?
a. The temperature of liquid refrigerant above its condensing
temperature
b. The difference between outdoor temperature and indoor
temperature
, c. The temperature of refrigerant vapor above its saturation
temperature at the same pressure
d. The temperature difference between compressor inlet and outlet air
Rationale: Superheat is calculated by subtracting the refrigerant's
saturation temperature at the measured pressure from the actual
vapor temperature. It indicates how much the vapor has been heated
beyond the point at which it completely evaporated.
6. What is subcooling in a refrigeration system?
a. Cooling refrigerant vapor below its dew point
b. Reducing compressor motor speed
c. Cooling liquid refrigerant below its saturation temperature at the
same pressure
d. Lowering evaporator pressure below the design value
Rationale: Subcooling is the temperature difference between the
liquid refrigerant's saturation temperature and its actual
temperature. Proper subcooling helps ensure that liquid refrigerant
reaches the metering device without unwanted flashing.
7. Which condition is most likely to cause excessively high compressor
discharge pressure?
Contractor Exam Questions and Correct
Answers (Verified Answers) Plus Rationale
2027 Q&A| Instant Download Pdf
1. What is the primary function of an evaporator in a vapor-
compression refrigeration system?
a. To reject heat from the refrigerant to the outdoor air
b. To increase the refrigerant pressure
c. To absorb heat from the space or material being cooled
d. To remove moisture from the compressor oil
Rationale: The evaporator absorbs heat from the conditioned space as
low-pressure refrigerant evaporates inside its coils. This heat
absorption produces the cooling effect. The condenser performs the
opposite function by rejecting heat to the surroundings.
,2. What is the primary purpose of a compressor in a refrigeration
system?
a. To reduce refrigerant pressure below atmospheric pressure
b. To remove moisture from the refrigerant
c. To compress refrigerant vapor, increasing its pressure and
temperature
d. To convert high-pressure liquid refrigerant into low-pressure liquid
Rationale: The compressor draws low-pressure refrigerant vapor from
the evaporator and compresses it into high-pressure, high-
temperature vapor. This allows the refrigerant to release heat in the
condenser and continue circulating through the system.
3. Which component removes heat from high-pressure refrigerant
vapor and converts it into liquid?
a. Evaporator
b. Expansion valve
c. Accumulator
d. Condenser
,Rationale: The condenser transfers heat from the refrigerant to
outdoor air or cooling water. As the refrigerant loses heat, it
condenses from vapor into liquid at approximately constant pressure.
4. What is the primary function of a thermostatic expansion valve
(TXV)?
a. To maintain a constant compressor discharge temperature
b. To regulate condenser fan speed
c. To control refrigerant flow into the evaporator in response to
superheat
d. To prevent refrigerant from entering the condenser
Rationale: A TXV regulates refrigerant flow based on evaporator
outlet superheat. It helps maintain effective evaporator utilization
while preventing excessive liquid refrigerant from returning to the
compressor.
5. What does superheat represent in a refrigeration system?
a. The temperature of liquid refrigerant above its condensing
temperature
b. The difference between outdoor temperature and indoor
temperature
, c. The temperature of refrigerant vapor above its saturation
temperature at the same pressure
d. The temperature difference between compressor inlet and outlet air
Rationale: Superheat is calculated by subtracting the refrigerant's
saturation temperature at the measured pressure from the actual
vapor temperature. It indicates how much the vapor has been heated
beyond the point at which it completely evaporated.
6. What is subcooling in a refrigeration system?
a. Cooling refrigerant vapor below its dew point
b. Reducing compressor motor speed
c. Cooling liquid refrigerant below its saturation temperature at the
same pressure
d. Lowering evaporator pressure below the design value
Rationale: Subcooling is the temperature difference between the
liquid refrigerant's saturation temperature and its actual
temperature. Proper subcooling helps ensure that liquid refrigerant
reaches the metering device without unwanted flashing.
7. Which condition is most likely to cause excessively high compressor
discharge pressure?
