1|Page
FDNY Z51 EXAM 2 NEWEST 2025 ACTUAL EXAM|
QUESTIONS AND CORRECT DETAILED ANSWERS
(VERIFIED ANSWERS) ALREADY GRADED A+
What is a superheated vapor? - ..(ANSWER)...completely dry vapor
In electrical circuits the conductor is always what color? - ..(ANSWER)...Green or
Bare
Unloaders are used for what? - ..(ANSWER)...To increase capacity
Oil foaming in a crankcase is caused by what? - ..(ANSWER)...A sudden drop in
crankcase pressure
How would you test for acid in the refrigerant? - ..(ANSWER)...Spraying liquid
refrigerant from a condenser or receiver on to bond paper
What is the function of a cylinder bypass? - ..(ANSWER)...To allow operation at
different capacities
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? -
..(ANSWER)...Yes. this temperature is too high for human comfort purpose
,2|Page
The packing gland of a centrifugal pump serves to: - ..(ANSWER)...The drip part of
the packing gland gives evidence that there is water in the pump
Capacity control of a reciprocating hermetic compressor is typically achieved
through - ..(ANSWER)...Operation of the hot gas bypass valve
The most important reason to sub-cool the refrigerant in the condenser is to
ensure that: - ..(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. - ..(ANSWER)...An expansion valve that is open to wide
A low side float valve is used to maintain: - ..(ANSWER)...The level of the
refrigerant in the evaporator
Regarding fire safety, which ASHRAE refrigerant safety classification indicates no
flammability and lower toxicity? - ..(ANSWER)...A1
All liquid has been recovered from a system to be overhauled, the system -
..(ANSWER)...Should not be opened until all vapor has been recovered
When a refrigerant engineer uses a portable compressor recovery unit to remove
vapor refrigerant from a refrigeration system the removal rate of the refrigerant
will gradually slow down because - ..(ANSWER)...The vapor density is decreasing
, 3|Page
You are the engineer running a 2000-ton (steam-driven turbine) centrifugal
refrigeration system, a refrigeration system supplies chilled water to a college
campus with multiple buildings. During the course of making your rounds, you
check the 9 cell cooling tower on the roof. You note the water level in all of the
cooling tower cells is very low. Which one of the following immediate action
would take? - ..(ANSWER)...Add additional make up water to cooling tower
A rooftop water cooling tower is connected to a water pump in the building
basement with a 12 inches diameter pipe, with the pump turn off, a pressure
gauge at the pumps inlet show a pressure of 140 PSIG the height of the water
column, in feet, would be closet to. - ..(ANSWER)...323
What device protects the steam turbine from excessive speed? -
..(ANSWER)...Governor assembly
A refrigeration compressor has failed to turn on. The refrigeration engineer on
duty verifies that the electrical circuit to the motor, including all switches and
circuit breakers, is complete according to recommended service practice, the next
item to be checked would likely be the: - ..(ANSWER)...Temperature and pressure
controls
Refrigerants are characterized by their physical properties included flashpoint,
refrigeration effect, and others. Of the refrigerants in commercial and industrial
the highest latent heat and refrigerant effect is: - ..(ANSWER)...Ammonia
On what characteristics is ASHRAE refrigerant safety group classification system: -
..(ANSWER)...flammability and toxicity
FDNY Z51 EXAM 2 NEWEST 2025 ACTUAL EXAM|
QUESTIONS AND CORRECT DETAILED ANSWERS
(VERIFIED ANSWERS) ALREADY GRADED A+
What is a superheated vapor? - ..(ANSWER)...completely dry vapor
In electrical circuits the conductor is always what color? - ..(ANSWER)...Green or
Bare
Unloaders are used for what? - ..(ANSWER)...To increase capacity
Oil foaming in a crankcase is caused by what? - ..(ANSWER)...A sudden drop in
crankcase pressure
How would you test for acid in the refrigerant? - ..(ANSWER)...Spraying liquid
refrigerant from a condenser or receiver on to bond paper
What is the function of a cylinder bypass? - ..(ANSWER)...To allow operation at
different capacities
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? -
..(ANSWER)...Yes. this temperature is too high for human comfort purpose
,2|Page
The packing gland of a centrifugal pump serves to: - ..(ANSWER)...The drip part of
the packing gland gives evidence that there is water in the pump
Capacity control of a reciprocating hermetic compressor is typically achieved
through - ..(ANSWER)...Operation of the hot gas bypass valve
The most important reason to sub-cool the refrigerant in the condenser is to
ensure that: - ..(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. - ..(ANSWER)...An expansion valve that is open to wide
A low side float valve is used to maintain: - ..(ANSWER)...The level of the
refrigerant in the evaporator
Regarding fire safety, which ASHRAE refrigerant safety classification indicates no
flammability and lower toxicity? - ..(ANSWER)...A1
All liquid has been recovered from a system to be overhauled, the system -
..(ANSWER)...Should not be opened until all vapor has been recovered
When a refrigerant engineer uses a portable compressor recovery unit to remove
vapor refrigerant from a refrigeration system the removal rate of the refrigerant
will gradually slow down because - ..(ANSWER)...The vapor density is decreasing
, 3|Page
You are the engineer running a 2000-ton (steam-driven turbine) centrifugal
refrigeration system, a refrigeration system supplies chilled water to a college
campus with multiple buildings. During the course of making your rounds, you
check the 9 cell cooling tower on the roof. You note the water level in all of the
cooling tower cells is very low. Which one of the following immediate action
would take? - ..(ANSWER)...Add additional make up water to cooling tower
A rooftop water cooling tower is connected to a water pump in the building
basement with a 12 inches diameter pipe, with the pump turn off, a pressure
gauge at the pumps inlet show a pressure of 140 PSIG the height of the water
column, in feet, would be closet to. - ..(ANSWER)...323
What device protects the steam turbine from excessive speed? -
..(ANSWER)...Governor assembly
A refrigeration compressor has failed to turn on. The refrigeration engineer on
duty verifies that the electrical circuit to the motor, including all switches and
circuit breakers, is complete according to recommended service practice, the next
item to be checked would likely be the: - ..(ANSWER)...Temperature and pressure
controls
Refrigerants are characterized by their physical properties included flashpoint,
refrigeration effect, and others. Of the refrigerants in commercial and industrial
the highest latent heat and refrigerant effect is: - ..(ANSWER)...Ammonia
On what characteristics is ASHRAE refrigerant safety group classification system: -
..(ANSWER)...flammability and toxicity
