FDNY z51 TEST QUESTIONS AND ANSWERS (VERIFIED AND WELL
FDNY z51 test
ELABORATED ANSWERS) LATEST UPDATE 2025/2026
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1. What is a superheated vapor? completely dry vapor
2. In electrical circuits the conductor is always what col- Green or Bare
or?
3. Unloaders are used for what? To increase capacity
4. Oil foaming in a crankcase is caused by what? A sudden drop in
crankcase pressure
5. How would you test for acid in the refrigerant? Spraying liquid refrigerant
from a condenser or re-
ceiver on to bond paper
6. What is the function of a cylinder bypass? To allow operation at dif-
ferent capacities
7. The chilled water supply to the building is 55F. If the Yes. this temperature is
chiller is being used for human comfort, should you too high for human com-
be concerned about this, and why? fort purpose
8. The packing gland of a centrifugal pump serves to: The drip part of the pack-
ing gland gives evidence
that there is water in the
pump
9. Capacity control of a reciprocating hermetic compres- Operation of the hot gas
sor is typically achieved through bypass valve
10. The most important reason to sub-cool the refrigerant A pure liquid refrigerant
in the condenser is to ensure that: will enter the metering
device
11.
, FDNY z51 test
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A refrigeration engineer is logging reading from a An expansion valve that is
reciprocating system. compressor discharge temper- open to wide
ature have dropped significantly and the suction line
pressure is high. which of the following that may be
causing this set of condition.
12. A low side float valve is used to maintain: The level of the refrigerant
in the evaporator
13. Regarding fire safety, which ASHRAE refrigerant safety A1
classification indicates no flammability and lower tox-
icity?
14. All liquid has been recovered from a system to be Should not be opened un-
overhauled, the system til all vapor has been re-
covered
15. When a refrigerant engineer uses a portable compres- The vapor density is de-
sor recovery unit to remove vapor refrigerant from a creasing
refrigeration system the removal rate of the refriger-
ant will gradually slow down because
16. You are the engineer running a 2000-ton (steam-dri- Add additional make up
ven turbine) centrifugal refrigeration system, a re- water to cooling tower
frigeration 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?
17. A rooftop water cooling tower is connected to a water 323
pump in the building basement with a 12 inches diam-
, FDNY z51 test
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eter 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.
18. What device protects the steam turbine from exces- Governor assembly
sive speed?
19. A refrigeration compressor has failed to turn on. The Temperature and pres-
refrigeration engineer on duty verifies that the electri- sure controls
cal circuit to the motor, including all switches and cir-
cuit breakers, is complete according to recommended
service practice, the next item to be checked would
likely be the:
20. Refrigerants are characterized by their physical prop- Ammonia
erties included flashpoint, refrigeration effect, and
others. Of the refrigerants in commercial and indus-
trial the highest latent heat and refrigerant effect is:
21. On what characteristics is ASHRAE refrigerant safety flammability and toxicity
group classification system:
22. Of the following, and example of an in-line refrigerant Refrigerant recycling
cleaning system that may be used with a centrifugal
compressor containing R123 refrigerant is:
23. Information about the physical and chemical proper- Material Safety Data Sheet
ties of a hazardous material can be found in:
24. What is the function of the turbine auxiliary oil pump? Establish oil pressure dur-
ing turbine start up
25. Compressor suction
FDNY z51 test
ELABORATED ANSWERS) LATEST UPDATE 2025/2026
Study online at https://quizlet.com/_heuktb
1. What is a superheated vapor? completely dry vapor
2. In electrical circuits the conductor is always what col- Green or Bare
or?
3. Unloaders are used for what? To increase capacity
4. Oil foaming in a crankcase is caused by what? A sudden drop in
crankcase pressure
5. How would you test for acid in the refrigerant? Spraying liquid refrigerant
from a condenser or re-
ceiver on to bond paper
6. What is the function of a cylinder bypass? To allow operation at dif-
ferent capacities
7. The chilled water supply to the building is 55F. If the Yes. this temperature is
chiller is being used for human comfort, should you too high for human com-
be concerned about this, and why? fort purpose
8. The packing gland of a centrifugal pump serves to: The drip part of the pack-
ing gland gives evidence
that there is water in the
pump
9. Capacity control of a reciprocating hermetic compres- Operation of the hot gas
sor is typically achieved through bypass valve
10. The most important reason to sub-cool the refrigerant A pure liquid refrigerant
in the condenser is to ensure that: will enter the metering
device
11.
, FDNY z51 test
Study online at https://quizlet.com/_heuktb
A refrigeration engineer is logging reading from a An expansion valve that is
reciprocating system. compressor discharge temper- open to wide
ature have dropped significantly and the suction line
pressure is high. which of the following that may be
causing this set of condition.
12. A low side float valve is used to maintain: The level of the refrigerant
in the evaporator
13. Regarding fire safety, which ASHRAE refrigerant safety A1
classification indicates no flammability and lower tox-
icity?
14. All liquid has been recovered from a system to be Should not be opened un-
overhauled, the system til all vapor has been re-
covered
15. When a refrigerant engineer uses a portable compres- The vapor density is de-
sor recovery unit to remove vapor refrigerant from a creasing
refrigeration system the removal rate of the refriger-
ant will gradually slow down because
16. You are the engineer running a 2000-ton (steam-dri- Add additional make up
ven turbine) centrifugal refrigeration system, a re- water to cooling tower
frigeration 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?
17. A rooftop water cooling tower is connected to a water 323
pump in the building basement with a 12 inches diam-
, FDNY z51 test
Study online at https://quizlet.com/_heuktb
eter 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.
18. What device protects the steam turbine from exces- Governor assembly
sive speed?
19. A refrigeration compressor has failed to turn on. The Temperature and pres-
refrigeration engineer on duty verifies that the electri- sure controls
cal circuit to the motor, including all switches and cir-
cuit breakers, is complete according to recommended
service practice, the next item to be checked would
likely be the:
20. Refrigerants are characterized by their physical prop- Ammonia
erties included flashpoint, refrigeration effect, and
others. Of the refrigerants in commercial and indus-
trial the highest latent heat and refrigerant effect is:
21. On what characteristics is ASHRAE refrigerant safety flammability and toxicity
group classification system:
22. Of the following, and example of an in-line refrigerant Refrigerant recycling
cleaning system that may be used with a centrifugal
compressor containing R123 refrigerant is:
23. Information about the physical and chemical proper- Material Safety Data Sheet
ties of a hazardous material can be found in:
24. What is the function of the turbine auxiliary oil pump? Establish oil pressure dur-
ing turbine start up
25. Compressor suction
