Z-51 Written Exam UPDATED ACTUAL
Exam Questions and CORRECT Answers
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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - D.
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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - C. 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 - CORRECT ANSWER - C. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - B. Yes,
this temperature is too high for humans comfort purpose
Exam Questions and CORRECT Answers
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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - D.
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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - C. 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 - CORRECT ANSWER - C. 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 - CORRECT ANSWER - A. 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 - CORRECT ANSWER - B. 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 - CORRECT ANSWER - D. 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 - CORRECT ANSWER - B. Yes,
this temperature is too high for humans comfort purpose
