FDNY Z51 WRITTEN EXAM ACTUAL EXAM
COMPLETE 200+ QUESTIONS WITH DETAILED
VERIFIED ANSWERS / ALREADY GRADED A+
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:
A. Raising the condenser liquid level to the maximum
B. Lowering the chilled water set point
C. Raising the condenser head pressure
D. Lowering the condensing pressure - ANSWERD. Lowering the condensing pressure
The heat removed from the refrigerant in a condenser is:
A. Sensible and latent heat
B. Latent heat only
C. Radiant heat only
D. Sensible heat only - ANSWERA. 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:
A. Do not weigh more than 200 pounds when filled
B. Are approved by the US Department of Transportation
C. Are approved by the OSHA Association
D. Do not exceed 55 Gallons in capacity - ANSWERB. Are approved by the US
Department of Transportation
Which of the following best describes how the cylinder unloader work?
A. Keep in the suction valve opened while the compressor is in the return stroke
B. Controls the clearance volume in the compressor with a solenoid
C. Controls the opening of the passage into the compressor with variable vanes
D. Unloads the piston to create less pressure - ANSWERA. Keep in the suction valve
opened while the compressor is in the return stroke
In the most semi Hermetic compressors, the suction vapor is used to:
A. Removes oil from the motor housing
B. Cools the motor
,C. Minimizes oil foaming
D. Removes oil foam from the shaft - ANSWERB. Cools the motor
The amount of refrigerant that flows through the orifices of a economizer is determined
by the:
A. Number of economizer stages
B. Temperature of the high side refrigerant
C. Number of compressor stages
D. Difference between high side and low side pressure - ANSWERD. Difference
between high side and low side pressure
The installation of an inline refrigerant cleaning system is advisable:
A. For high pressure refrigerant systems
B. To purge non-condensables
C. For systems using toxic refrigerant
D. To remove impurities from the system - ANSWERD. To remove impurities from the
system
The type of refrigerant system that is least likely to leak refrigerant into the building
space that are being cooled:
A. The direct vented closed system
B. The direct closed system
C. Any system using reciprocating compressor
D. The indirect system - ANSWERD. The indirect system
The suction pressure of a reciprocating compressor is 65 PSIG. The discharge pressure
of this compressor is 120 PSIG. The atmospheric is 14.7 PSI. The compression ratio for
the given condition is closet to:
A. 2.07
B. 4.41
C. 1.69
D. 1.84 - ANSWERC. 1.69
A superheated vapor is a:
A. Dry vapor at the saturation temperature
B. Dry saturated vapor
C. Dry vapor above the saturation temperature
D. Vapor with minimal amount of included liquid - ANSWERC. Dry vapor above the
saturation temperature
,A refrigerant engineer verifies that a condenser water pump is cavitating. Of the
following the most likely cause for this condition is:
A. A faulty cooling tower water level controller
B. Operating at sustaining high loads
C. Too long a period between pump servicing
D. Refrigerant leaks through the pumps packing - ANSWERA. A faulty cooling tower
water level controller
A centrifugal water pump is known as a lift pump when the:
A. The pump lifts the water into the pump upon startup
B. The water supply to the pump suction inlet is below the pump level
C. The discharge head exceed 150 feet
D. The pump is started with the suction valve open - ANSWERB. The water supply to
the pump suction inlet is below the pump level
A TXV is used to maintain constant:
A. Refrigerant flow
B. Evaporator pressure
C. Evaporator pressure drop
D. Evaporator superheat - ANSWERD. Evaporator superheat
The chilled water supply to the building is 55° F. IF the chiller is being used for humans
comfort, should you be concerned about this, and why?
A. Yes, this temperature is too low for human comfort purpose
B. Yes, this temperature is too high for humans comfort purpose
C. No, 55° F is within an acceptable range
D. No, temperature gauges often give false high readings - ANSWERB. Yes, this
temperature is too high for humans comfort purpose
The packing gland of a centrifugal pump serves to:
A. Keep the bearing cooled
B. Keeps air out of the pumps when the impeller housing is under negative pressure
C. The drip part of the packing gland gives evidence that there is water in the pump
D. All of the answers are correct - ANSWERC. 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:
A. Regulating the opening of the discharge valve
B. Variation of the condenser water temperature
C. Regulating the opening of the TXV
, D. Operation of the hot gas bypass valve - ANSWERD. Operation of the hot gas bypass
valve
The most important reason to sub-cool the refrigerant in the condenser is to ensure that:
A. A pure liquid refrigerant will enter the metering device
B. Liquid slugs will not enter the compressor
C. The condenser is working efficiently
D. The cooling tower has sufficient water - ANSWERA. A pure liquid refrigerant will
enter the metering device
A refrigeration engineer is logging readings from a reciprocating system, compressor
discharge temperatures have dropped significantly, and the suction line pressure is
high, which of the following that may be causing this set of condition.
A. Compressor cycle
B. An expansion valve that is open to wide
C. Malfunction of a unloader
D. An expansion valve that is closed to much - ANSWERB. An expansion valve that is
open to wide
A low side float valve is used to maintain:
A. A constant refrigerant flow
B. The water level in the cooling towers
C. The level of refrigerant in the condenser
D. The level of the refrigerant in the evaporator - ANSWERD. The level of the refrigerant
in the evaporator
Regarding safety, which ASHRAE refrigerant safety classification indicates no
flammability and lower toxicity?
A. A3
B. A1
C. B1
D. B2 - ANSWERB. A1
When an expansion valve is operating properly, at the end of the evaporator will
contain:
A. Saturated liquid refrigerant
B. Only liquid refrigerant
C. Only vapor
D. Only superheated vapor - ANSWERD. Only superheated vapor
What information is not contained in a Material Safety Data Sheet-MSDS?
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