FDNY Z-51 Review Test – 2026/2027 Updated
Practice Questions and Verified Answers with
Explanations
1. The most important reason to sub-cool the refrigerant in the condenser is
to ensure that:
A) The refrigerant is fully vaporized
B) A pure liquid refrigerant will enter the metering device
C) The compressor runs cooler
D) The evaporator pressure increases
Answer B: A pure liquid refrigerant will enter the metering device
Rationale: Subcooling ensures a solid column of liquid refrigerant enters the
expansion valve for proper metering.
2. What does sub-cooling ensure in a refrigeration system?
A) A pure liquid flows to the metering device
B) The evaporator is fully flooded
C) The compressor receives liquid refrigerant
D) The condenser pressure is reduced
Answer A: A pure liquid flows to the metering device
Rationale: Subcooling prevents flash gas in the liquid line, ensuring proper
expansion valve operation.
,3. What pressure is R-22 at 38°F on a PT chart?
A) 50.2 PSI
B) 65.6 PSI
C) 72.4 PSI
D) 85.3 PSI
Answer B: 65.6 PSI
Rationale: At 38°F, R-22 has a saturation pressure of approximately 65.6 PSI on a
standard PT chart.
4. What does the chiller's purge unit do?
A) It removes oil from the refrigerant
B) It removes air and non-condensables from the condenser
C) It purges moisture from the system
D) It evacuates refrigerant for storage
Answer B: It removes air and non-condensables from the condenser
Rationale: The purge unit extracts air and non-condensable gases that reduce
condenser efficiency.
5. The heat removed from the refrigerant in a condenser is:
A) Only sensible heat
B) Only latent heat
,C) Sensible and latent heat
D) Superheat only
Answer C: Sensible and latent heat
Rationale: The condenser removes both sensible heat (cooling vapor) and latent
heat (condensing).
6. Liquid refrigerant that has passed through a metering device is at:
A) High pressure saturated vapor
B) Low pressure saturated liquid
C) Low pressure superheated vapor
D) High pressure subcooled liquid
Answer B: Low pressure saturated liquid
Rationale: The expansion valve reduces pressure, creating a low-pressure
saturated liquid-vapor mixture.
7. What can overcharge of refrigerant cause?
A) Low discharge pressure
B) High discharge pressure
C) Low suction pressure
D) Oil foaming only
Answer B: High discharge pressure
Rationale: Excess refrigerant in the system raises condensing pressure and
compressor discharge pressure.
, 8. What is the purpose of the muffler on a refrigeration machine?
A) It silences the discharge gas pulsations and is located on the discharge line
B) It reduces suction line noise
C) It filters refrigerant
D) It stores oil
Answer A: It silences the discharge gas pulsations and is located on the
discharge line
Rationale: The muffler is placed on the discharge line between the compressor
and condenser, as close to the compressor as possible.
9. Where is the muffler located?
A) On the suction line before the compressor
B) On the discharge line between the compressor and condenser
C) On the liquid line after the receiver
D) In the evaporator outlet
Answer B: On the discharge line between the compressor and condenser
Rationale: The muffler is positioned as close to the compressor as possible on the
discharge line.
10. Define superheated vapor.
A) Wet vapor below saturation temperature
Practice Questions and Verified Answers with
Explanations
1. The most important reason to sub-cool the refrigerant in the condenser is
to ensure that:
A) The refrigerant is fully vaporized
B) A pure liquid refrigerant will enter the metering device
C) The compressor runs cooler
D) The evaporator pressure increases
Answer B: A pure liquid refrigerant will enter the metering device
Rationale: Subcooling ensures a solid column of liquid refrigerant enters the
expansion valve for proper metering.
2. What does sub-cooling ensure in a refrigeration system?
A) A pure liquid flows to the metering device
B) The evaporator is fully flooded
C) The compressor receives liquid refrigerant
D) The condenser pressure is reduced
Answer A: A pure liquid flows to the metering device
Rationale: Subcooling prevents flash gas in the liquid line, ensuring proper
expansion valve operation.
,3. What pressure is R-22 at 38°F on a PT chart?
A) 50.2 PSI
B) 65.6 PSI
C) 72.4 PSI
D) 85.3 PSI
Answer B: 65.6 PSI
Rationale: At 38°F, R-22 has a saturation pressure of approximately 65.6 PSI on a
standard PT chart.
4. What does the chiller's purge unit do?
A) It removes oil from the refrigerant
B) It removes air and non-condensables from the condenser
C) It purges moisture from the system
D) It evacuates refrigerant for storage
Answer B: It removes air and non-condensables from the condenser
Rationale: The purge unit extracts air and non-condensable gases that reduce
condenser efficiency.
5. The heat removed from the refrigerant in a condenser is:
A) Only sensible heat
B) Only latent heat
,C) Sensible and latent heat
D) Superheat only
Answer C: Sensible and latent heat
Rationale: The condenser removes both sensible heat (cooling vapor) and latent
heat (condensing).
6. Liquid refrigerant that has passed through a metering device is at:
A) High pressure saturated vapor
B) Low pressure saturated liquid
C) Low pressure superheated vapor
D) High pressure subcooled liquid
Answer B: Low pressure saturated liquid
Rationale: The expansion valve reduces pressure, creating a low-pressure
saturated liquid-vapor mixture.
7. What can overcharge of refrigerant cause?
A) Low discharge pressure
B) High discharge pressure
C) Low suction pressure
D) Oil foaming only
Answer B: High discharge pressure
Rationale: Excess refrigerant in the system raises condensing pressure and
compressor discharge pressure.
, 8. What is the purpose of the muffler on a refrigeration machine?
A) It silences the discharge gas pulsations and is located on the discharge line
B) It reduces suction line noise
C) It filters refrigerant
D) It stores oil
Answer A: It silences the discharge gas pulsations and is located on the
discharge line
Rationale: The muffler is placed on the discharge line between the compressor
and condenser, as close to the compressor as possible.
9. Where is the muffler located?
A) On the suction line before the compressor
B) On the discharge line between the compressor and condenser
C) On the liquid line after the receiver
D) In the evaporator outlet
Answer B: On the discharge line between the compressor and condenser
Rationale: The muffler is positioned as close to the compressor as possible on the
discharge line.
10. Define superheated vapor.
A) Wet vapor below saturation temperature
