FDNY Z-51 REFRIGERATION
ENGINEER EXAM PREP: 500
LATEST QUESTIONS, ANSWERS &
RATIONALES (2026 EDITION)
FDNY Z-51 Refrigeration Engineer — Practice Test Bank
1. What is the primary purpose of a refrigeration system?
A. To generate electricity
B. To transfer heat from a lower-temperature space to a higher-temperature sink
C. To increase humidity in a conditioned space
D. To convert mechanical energy directly into light
Answer: B. To transfer heat from a lower-temperature space to a higher-temperature sink.
Rationale: Refrigeration systems remove heat from a space or substance that is being cooled
and reject that heat to a warmer environment, typically through the condenser.
2. Which component normally removes heat from the refrigerated space?
A. Condenser
B. Compressor
C. Evaporator
D. Receiver
Answer: C. Evaporator.
Rationale: The evaporator absorbs heat from the space, product, or fluid being cooled as
refrigerant evaporates inside the evaporator.
3. What is the primary function of the compressor in a vapor-compression refrigeration
system?
A. Reduce refrigerant pressure
B. Increase refrigerant pressure and circulate refrigerant
C. Remove moisture from the air
D. Store liquid refrigerant
,Answer: B. Increase refrigerant pressure and circulate refrigerant.
Rationale: The compressor receives low-pressure refrigerant vapor from the evaporator and
compresses it into a high-pressure, high-temperature vapor before it enters the condenser.
4. Which component rejects heat from the refrigerant to the surrounding medium?
A. Evaporator
B. Expansion valve
C. Condenser
D. Accumulator
Answer: C. Condenser.
Rationale: The condenser removes heat from the high-pressure refrigerant vapor, causing it
to condense into a liquid.
5. What happens to refrigerant pressure as it passes through a typical expansion
device?
A. It increases substantially
B. It remains constant
C. It decreases substantially
D. It becomes atmospheric pressure
Answer: C. It decreases substantially.
Rationale: The expansion device creates a pressure drop between the high-pressure liquid
side and the low-pressure evaporator side.
6. Which device is commonly used to regulate refrigerant flow into an evaporator based
on superheat?
A. Thermostatic expansion valve
B. Check valve
C. Relief valve
D. Service valve
Answer: A. Thermostatic expansion valve.
Rationale: A TXV regulates refrigerant flow according to evaporator outlet superheat,
helping maintain appropriate evaporator operation and protecting the compressor from
excessive liquid return.
,7. What is superheat?
A. Temperature of a liquid below its boiling point
B. Temperature of a vapor above its saturation temperature at a given pressure
C. Pressure above the design pressure
D. Heat contained only in liquid refrigerant
Answer: B. Temperature of a vapor above its saturation temperature at a given pressure.
Rationale: Superheat indicates how far a vapor has been heated above its saturation
temperature.
8. What is subcooling?
A. Cooling a liquid below its saturation temperature
B. Heating a vapor above saturation temperature
C. Increasing evaporator pressure
D. Reducing compressor capacity
Answer: A. Cooling a liquid below its saturation temperature.
Rationale: Subcooling occurs when liquid refrigerant is cooled below its saturation
temperature at the corresponding pressure.
9. Why is excessive liquid refrigerant entering a reciprocating compressor dangerous?
A. It can cause liquid slugging and mechanical damage
B. It always increases compressor efficiency
C. It increases condenser capacity
D. It eliminates oil circulation
Answer: A. It can cause liquid slugging and mechanical damage.
Rationale: Compressors are designed primarily to compress vapor. Liquid entering the
cylinder can produce hydraulic shock and damage valves, pistons, connecting rods, or other
components.
10. What is the primary purpose of a refrigerant receiver?
A. Increase evaporator temperature
B. Store liquid refrigerant
, C. Remove oil from the compressor
D. Increase suction pressure
Answer: B. Store liquid refrigerant.
Rationale: A receiver provides storage for liquid refrigerant and helps accommodate
changes in system charge and operating conditions.
11. Which compressor type uses rotating impellers to impart velocity to refrigerant
vapor?
A. Reciprocating
B. Screw
C. Centrifugal
D. Scroll
Answer: C. Centrifugal.
Rationale: A centrifugal compressor uses rotating impellers to accelerate refrigerant vapor
and convert velocity into pressure.
12. What condition is commonly associated with refrigerant floodback to a compressor?
A. Excessive superheat
B. Insufficient evaporator superheat
C. Excessive condenser subcooling only
D. High compressor discharge temperature only
Answer: B. Insufficient evaporator superheat.
Rationale: Low superheat can indicate that liquid refrigerant is leaving the evaporator and
returning toward the compressor, potentially causing floodback.
13. What is the main purpose of compressor lubrication oil?
A. Increase refrigerant pressure
B. Reduce friction and wear between moving components
C. Replace refrigerant
D. Remove heat from the condenser
Answer: B. Reduce friction and wear between moving components.
Rationale: Refrigeration oil lubricates bearings, shafts, pistons, and other moving
components while also helping remove heat from some compressor parts.
ENGINEER EXAM PREP: 500
LATEST QUESTIONS, ANSWERS &
RATIONALES (2026 EDITION)
FDNY Z-51 Refrigeration Engineer — Practice Test Bank
1. What is the primary purpose of a refrigeration system?
A. To generate electricity
B. To transfer heat from a lower-temperature space to a higher-temperature sink
C. To increase humidity in a conditioned space
D. To convert mechanical energy directly into light
Answer: B. To transfer heat from a lower-temperature space to a higher-temperature sink.
Rationale: Refrigeration systems remove heat from a space or substance that is being cooled
and reject that heat to a warmer environment, typically through the condenser.
2. Which component normally removes heat from the refrigerated space?
A. Condenser
B. Compressor
C. Evaporator
D. Receiver
Answer: C. Evaporator.
Rationale: The evaporator absorbs heat from the space, product, or fluid being cooled as
refrigerant evaporates inside the evaporator.
3. What is the primary function of the compressor in a vapor-compression refrigeration
system?
A. Reduce refrigerant pressure
B. Increase refrigerant pressure and circulate refrigerant
C. Remove moisture from the air
D. Store liquid refrigerant
,Answer: B. Increase refrigerant pressure and circulate refrigerant.
Rationale: The compressor receives low-pressure refrigerant vapor from the evaporator and
compresses it into a high-pressure, high-temperature vapor before it enters the condenser.
4. Which component rejects heat from the refrigerant to the surrounding medium?
A. Evaporator
B. Expansion valve
C. Condenser
D. Accumulator
Answer: C. Condenser.
Rationale: The condenser removes heat from the high-pressure refrigerant vapor, causing it
to condense into a liquid.
5. What happens to refrigerant pressure as it passes through a typical expansion
device?
A. It increases substantially
B. It remains constant
C. It decreases substantially
D. It becomes atmospheric pressure
Answer: C. It decreases substantially.
Rationale: The expansion device creates a pressure drop between the high-pressure liquid
side and the low-pressure evaporator side.
6. Which device is commonly used to regulate refrigerant flow into an evaporator based
on superheat?
A. Thermostatic expansion valve
B. Check valve
C. Relief valve
D. Service valve
Answer: A. Thermostatic expansion valve.
Rationale: A TXV regulates refrigerant flow according to evaporator outlet superheat,
helping maintain appropriate evaporator operation and protecting the compressor from
excessive liquid return.
,7. What is superheat?
A. Temperature of a liquid below its boiling point
B. Temperature of a vapor above its saturation temperature at a given pressure
C. Pressure above the design pressure
D. Heat contained only in liquid refrigerant
Answer: B. Temperature of a vapor above its saturation temperature at a given pressure.
Rationale: Superheat indicates how far a vapor has been heated above its saturation
temperature.
8. What is subcooling?
A. Cooling a liquid below its saturation temperature
B. Heating a vapor above saturation temperature
C. Increasing evaporator pressure
D. Reducing compressor capacity
Answer: A. Cooling a liquid below its saturation temperature.
Rationale: Subcooling occurs when liquid refrigerant is cooled below its saturation
temperature at the corresponding pressure.
9. Why is excessive liquid refrigerant entering a reciprocating compressor dangerous?
A. It can cause liquid slugging and mechanical damage
B. It always increases compressor efficiency
C. It increases condenser capacity
D. It eliminates oil circulation
Answer: A. It can cause liquid slugging and mechanical damage.
Rationale: Compressors are designed primarily to compress vapor. Liquid entering the
cylinder can produce hydraulic shock and damage valves, pistons, connecting rods, or other
components.
10. What is the primary purpose of a refrigerant receiver?
A. Increase evaporator temperature
B. Store liquid refrigerant
, C. Remove oil from the compressor
D. Increase suction pressure
Answer: B. Store liquid refrigerant.
Rationale: A receiver provides storage for liquid refrigerant and helps accommodate
changes in system charge and operating conditions.
11. Which compressor type uses rotating impellers to impart velocity to refrigerant
vapor?
A. Reciprocating
B. Screw
C. Centrifugal
D. Scroll
Answer: C. Centrifugal.
Rationale: A centrifugal compressor uses rotating impellers to accelerate refrigerant vapor
and convert velocity into pressure.
12. What condition is commonly associated with refrigerant floodback to a compressor?
A. Excessive superheat
B. Insufficient evaporator superheat
C. Excessive condenser subcooling only
D. High compressor discharge temperature only
Answer: B. Insufficient evaporator superheat.
Rationale: Low superheat can indicate that liquid refrigerant is leaving the evaporator and
returning toward the compressor, potentially causing floodback.
13. What is the main purpose of compressor lubrication oil?
A. Increase refrigerant pressure
B. Reduce friction and wear between moving components
C. Replace refrigerant
D. Remove heat from the condenser
Answer: B. Reduce friction and wear between moving components.
Rationale: Refrigeration oil lubricates bearings, shafts, pistons, and other moving
components while also helping remove heat from some compressor parts.
