1 | Page
FDNY Z51 WRITTEN EXAM 2025 UPDATED
ACTUAL EXAM WITH CORRECT SOLUTIONS.
The efficiency of the refrigerant cycle is affected by the
operation of the condenser. of the following. a more efficient
centrifugal compressor operation results from: - correct answer-
Lowering the condensing pressure
The heat removed from the refrigerant in a condenser is: -
correct answer- Sensible and latent heat
The refrigerant unit that you have been assigned to is being
taken out of service for a major repair. you have been assigned
to withdraw refrigerant for storage in suitable containers.
according to the new York city fire code, you must ensure that
the containers: - correct answer- Are approved by the US
department of transportation
Which of the following best describes how the cylinder unloader
work? - correct answer- Keep in the suction valve opened while
the compressor is in the return stroke
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In most semi hermetic compressors, the suction vapor is used
to: - correct answer- Cool the motor
The amount of refrigerant that flows through the orifices of a
economizer is determined by the: - correct answer- Difference
between the high side and load side pressure
The installation of an inline refrigerant cleaning system is
advisable: - correct answer- To remove impurities from the
system
The type of refrigerant system that is least likely to leak
refrigerant into the building space that are cooled - correct
answer- The indirect system
The suction pressure of a reciprocating compressor is 65PSIG.
the discharge pressure of this compressor is 120PSIG. the
atmospheric is 14.7 PSI. the compression ratio for the given
condition is closet to: - correct answer- 1.69
A super heated vapor is a ? - correct answer- Dry vapor above
the saturation temperature
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A refrigerant engineer verifies that a condenser water pump is
cavitating. of the following the most likely cause for this
condition is: - correct answer- A faulty cooling tower water level
controller
A centrifugal water pump is known as a lift pump when the: -
correct answer- The water supply to the pump suction inlet is
below the pump level
A TXV is used to maintain constant: - correct answer-
Evaporator superheat
The chilled water supply to the building is 55F. if the chiller is
being used for human comfort, should you be concerned about
this , and why? - correct answer- Yes, this temperature is too
high for human comfort purpose
The packing gland of a centrifugal pump serves to: - correct
answer- The drip part of the packing gland gives evidence that
there is water in the pump
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Capacity control of a reciprocating hermetic compressor is
typically achieved through - correct answer- Operation of the
hot gas bypass valve
The most important reason to sub-cool the refrigerant in the
condenser is to ensure that: - correct answer- A pure liquid
refrigerant will enter the metering device
A refrigeration engineer is logging reading from a reciprocating
system. compressor discharge temperature have dropped
significantly and the suction line pressure is high. which of the
following that may be causing this set of condition. - correct
answer- An expansion valve that is open to wide
A low side float valve is used to maintain: - correct answer- The
level of the refrigerant in the evaporator
Regarding fire safety, which ASHARE refrigerant safety
classification indicates no flammability and lower the toxicity? -
correct answer- A1
When an expansion valve is operating properly, at the end of
the evaporator will contain: - correct answer- Only superheated
vapor
FDNY Z51 WRITTEN EXAM 2025 UPDATED
ACTUAL EXAM WITH CORRECT SOLUTIONS.
The efficiency of the refrigerant cycle is affected by the
operation of the condenser. of the following. a more efficient
centrifugal compressor operation results from: - correct answer-
Lowering the condensing pressure
The heat removed from the refrigerant in a condenser is: -
correct answer- Sensible and latent heat
The refrigerant unit that you have been assigned to is being
taken out of service for a major repair. you have been assigned
to withdraw refrigerant for storage in suitable containers.
according to the new York city fire code, you must ensure that
the containers: - correct answer- Are approved by the US
department of transportation
Which of the following best describes how the cylinder unloader
work? - correct answer- Keep in the suction valve opened while
the compressor is in the return stroke
,2 | Page
In most semi hermetic compressors, the suction vapor is used
to: - correct answer- Cool the motor
The amount of refrigerant that flows through the orifices of a
economizer is determined by the: - correct answer- Difference
between the high side and load side pressure
The installation of an inline refrigerant cleaning system is
advisable: - correct answer- To remove impurities from the
system
The type of refrigerant system that is least likely to leak
refrigerant into the building space that are cooled - correct
answer- The indirect system
The suction pressure of a reciprocating compressor is 65PSIG.
the discharge pressure of this compressor is 120PSIG. the
atmospheric is 14.7 PSI. the compression ratio for the given
condition is closet to: - correct answer- 1.69
A super heated vapor is a ? - correct answer- Dry vapor above
the saturation temperature
,3 | Page
A refrigerant engineer verifies that a condenser water pump is
cavitating. of the following the most likely cause for this
condition is: - correct answer- A faulty cooling tower water level
controller
A centrifugal water pump is known as a lift pump when the: -
correct answer- The water supply to the pump suction inlet is
below the pump level
A TXV is used to maintain constant: - correct answer-
Evaporator superheat
The chilled water supply to the building is 55F. if the chiller is
being used for human comfort, should you be concerned about
this , and why? - correct answer- Yes, this temperature is too
high for human comfort purpose
The packing gland of a centrifugal pump serves to: - correct
answer- The drip part of the packing gland gives evidence that
there is water in the pump
, 4 | Page
Capacity control of a reciprocating hermetic compressor is
typically achieved through - correct answer- Operation of the
hot gas bypass valve
The most important reason to sub-cool the refrigerant in the
condenser is to ensure that: - correct answer- A pure liquid
refrigerant will enter the metering device
A refrigeration engineer is logging reading from a reciprocating
system. compressor discharge temperature have dropped
significantly and the suction line pressure is high. which of the
following that may be causing this set of condition. - correct
answer- An expansion valve that is open to wide
A low side float valve is used to maintain: - correct answer- The
level of the refrigerant in the evaporator
Regarding fire safety, which ASHARE refrigerant safety
classification indicates no flammability and lower the toxicity? -
correct answer- A1
When an expansion valve is operating properly, at the end of
the evaporator will contain: - correct answer- Only superheated
vapor
