FDNY Z51/ Z-51 REFRIGERATION EXAM (2025)
comprehensive ques%ons and verified answers (
detailed & elaborated) ACTUAL EXAM 2025 TEST!!
Efficiency of the refrigerant cycle is affected by the opera ons of the condenser. Of the
following, a more efficient centrifugal compressor opera on results from:
Lowering the condensing pressure
The heat removed from the refrigerant in a condenser is:
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 NYC Fire Code, you must ensure that the containers:
Are approved by the US Dept. of Transporta on
Which of the following best describes how the cylinder unloader works?
Keep in the suc on valve opened while the compressor is in the return stroke
In most semi-herme c compressors, the suc on vapor is used to:
Cool the motor
The amount of refrigerant that flows through the orifices of an economizer is determined by
the:
Differences between the high side and low side pressure
The installa on of an inline refrigerant cleaning system is advisable:
To remove impuri es from the system
The type of refrigerant system that is least likely to leak refrigerant into the building space that
are being cooled:
Indirect system
,The suc on pressure of a reciproca ng compressor is 65 PSIG. The discharge pressure of this
compressor is 120 PSIG. The atmospheric is 14.7 PSI. The compression ra o for the given
condi on is closest to:
1.69
A superheated vapor is:
Dry vapor above the satura on temperature
A refrigerant engineer verifies that a condenser water pump is cavita ng. Of the following, the
most likely cause for this condi on is:
A faulty cooling tower water level controller
A centrifugal water pump is known as a li= pump when the:
The water supply to the pump suc on inlet is below the pump level
A TXV is used to maintain constant:
Evaporator superheat
The chilled water supply to the building is 55 deg F. If the chiller is being used for human
comfort, should you be concerned about this, and why?
Yes, this temp is too high for human comfort purposes
The packing gland of a centrifugal pump serves to:
The drip part of the packing gland gives evidence that there is water in the pump
Capacity control of reciproca ng herme c compressor is typically achieved through:
Opera on of the hot gas bypass valve
The most important reason to sub-cool the refrigerant in the condenser is to ensure that:
A pure liquid refrigerant will enter the metering device
A refrigera on engineer is logging readings from a reciproca ng system. Compressor discharge
temperature have dropped significantly and the suc on line pressure is high. Which of the
following that may be causing this set of condi on?
An expansion valve that is open too wide
A low side float valve is used to maintain:
The level of the refrigerant in the evaporator
, Regarding fire safety, which ASHRAE refrigerant safety classifica on indicates no flammability
and lower toxicity?
A1
When an expansion valve is opera ng properly, at the end of the evaporator will contain:
Only superheated vapor
What informa on is not contained in a Material Safety Data Sheet?
Cost of the material
In a steam turbine, what is the func on of the Kingsbury thrust bearing?
Maintain axial posi oning of the rotor sha=
A centrifugal water pump is considered to the fully primed when?
The pump is full of liquid
Copper tubing refrigerant lines must be installed for a new system. It is a well known service
prac ce that tubing collapses at bends that must be made, the refrigerant engineer should use?
Level type tubing bender
A reciproca ng compressor is making a knocking sound during opera on. If the refrigerant worn
parts are not causing the knocking, what probably the cause?
Slugging of the liquid refrigerant
In order for a refrigerant to become superheated, it must be heated in a sec on of the low side
refrigerant line:
Where no liquid refrigerant is present
All liquid has been recovered from a system to be overhauled, the system:
Should not be opened un l all vapor has been recovered
When a refrigerant engineer uses a portable compressor recovery unit to remove vapor
refrigerant from a refrigera on system the removal rate of the refrigerant will gradually slow
down because?
The compressor efficiency is decreasing
You are the engineer running a 2000-ton (steam driven turbine) centrifugal refrigera on system,
a refrigera on system supplies chilled water to a college campus with mul ple buildings. During
comprehensive ques%ons and verified answers (
detailed & elaborated) ACTUAL EXAM 2025 TEST!!
Efficiency of the refrigerant cycle is affected by the opera ons of the condenser. Of the
following, a more efficient centrifugal compressor opera on results from:
Lowering the condensing pressure
The heat removed from the refrigerant in a condenser is:
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 NYC Fire Code, you must ensure that the containers:
Are approved by the US Dept. of Transporta on
Which of the following best describes how the cylinder unloader works?
Keep in the suc on valve opened while the compressor is in the return stroke
In most semi-herme c compressors, the suc on vapor is used to:
Cool the motor
The amount of refrigerant that flows through the orifices of an economizer is determined by
the:
Differences between the high side and low side pressure
The installa on of an inline refrigerant cleaning system is advisable:
To remove impuri es from the system
The type of refrigerant system that is least likely to leak refrigerant into the building space that
are being cooled:
Indirect system
,The suc on pressure of a reciproca ng compressor is 65 PSIG. The discharge pressure of this
compressor is 120 PSIG. The atmospheric is 14.7 PSI. The compression ra o for the given
condi on is closest to:
1.69
A superheated vapor is:
Dry vapor above the satura on temperature
A refrigerant engineer verifies that a condenser water pump is cavita ng. Of the following, the
most likely cause for this condi on is:
A faulty cooling tower water level controller
A centrifugal water pump is known as a li= pump when the:
The water supply to the pump suc on inlet is below the pump level
A TXV is used to maintain constant:
Evaporator superheat
The chilled water supply to the building is 55 deg F. If the chiller is being used for human
comfort, should you be concerned about this, and why?
Yes, this temp is too high for human comfort purposes
The packing gland of a centrifugal pump serves to:
The drip part of the packing gland gives evidence that there is water in the pump
Capacity control of reciproca ng herme c compressor is typically achieved through:
Opera on of the hot gas bypass valve
The most important reason to sub-cool the refrigerant in the condenser is to ensure that:
A pure liquid refrigerant will enter the metering device
A refrigera on engineer is logging readings from a reciproca ng system. Compressor discharge
temperature have dropped significantly and the suc on line pressure is high. Which of the
following that may be causing this set of condi on?
An expansion valve that is open too wide
A low side float valve is used to maintain:
The level of the refrigerant in the evaporator
, Regarding fire safety, which ASHRAE refrigerant safety classifica on indicates no flammability
and lower toxicity?
A1
When an expansion valve is opera ng properly, at the end of the evaporator will contain:
Only superheated vapor
What informa on is not contained in a Material Safety Data Sheet?
Cost of the material
In a steam turbine, what is the func on of the Kingsbury thrust bearing?
Maintain axial posi oning of the rotor sha=
A centrifugal water pump is considered to the fully primed when?
The pump is full of liquid
Copper tubing refrigerant lines must be installed for a new system. It is a well known service
prac ce that tubing collapses at bends that must be made, the refrigerant engineer should use?
Level type tubing bender
A reciproca ng compressor is making a knocking sound during opera on. If the refrigerant worn
parts are not causing the knocking, what probably the cause?
Slugging of the liquid refrigerant
In order for a refrigerant to become superheated, it must be heated in a sec on of the low side
refrigerant line:
Where no liquid refrigerant is present
All liquid has been recovered from a system to be overhauled, the system:
Should not be opened un l all vapor has been recovered
When a refrigerant engineer uses a portable compressor recovery unit to remove vapor
refrigerant from a refrigera on system the removal rate of the refrigerant will gradually slow
down because?
The compressor efficiency is decreasing
You are the engineer running a 2000-ton (steam driven turbine) centrifugal refrigera on system,
a refrigera on system supplies chilled water to a college campus with mul ple buildings. During
