FDNY Z-51 REFRIGERATION ENGINEER EXAM – 200
EXAM QUESTIONS COMPLETE WITH 100% VERIFIED
ANSWERS
1. What is the primary function of a compressor in a vapor-
compression refrigeration system?
A) To absorb heat from the refrigerated space
B) To raise the pressure and temperature of the refrigerant vapor
C) To reject heat to the ambient air or water
D) To meter liquid refrigerant into the evaporator
Correct Answer: B
Rationale: The compressor is the "heart" of the system. Its primary
function is to draw in low-pressure, low-temperature refrigerant vapor
from the evaporator and compress it into a high-pressure, high-
temperature vapor that can be condensed in the condenser. Options A,
C, and D describe the functions of the evaporator, condenser, and
expansion device, respectively.
2. According to ASHRAE Standard 34, what do the letters and numbers
in a refrigerant safety classification (e.g., A1, B2) represent?
A) The first character represents flammability; the second represents
toxicity.
B) The first character represents toxicity; the second represents
flammability.
C) The number represents the refrigerant's ozone depletion potential.
D) The letters indicate the refrigerant's chemical family.
,Correct Answer: B
Rationale: ASHRAE Standard 34 classifies refrigerants by toxicity (Class
A = lower toxicity, Class B = higher toxicity) and flammability (Class 1 =
no flame propagation, 2L = lower flammability, 2 = moderate, 3 = high).
Option B correctly identifies this order. Option A reverses the order.
3. What is the function of a Kingsbury thrust bearing in a steam
turbine?
A) To maintain first-stage steam pressure
B) To compensate for coupling misalignment
C) To maintain the axial positioning of the rotor shaft
D) To adjust shaft torque during startup
Correct Answer: C
Rationale: The Kingsbury thrust bearing is a type of tilting-pad thrust
bearing used to absorb axial thrust loads and maintain the precise axial
positioning of the rotor shaft. It does not maintain pressure or
compensate for misalignment. Options A, B, and D are incorrect.
4. Which component in a refrigeration system is specifically designed
to prevent liquid refrigerant from entering the compressor suction
inlet during operation?
A) Liquid receiver
B) Suction line accumulator
C) Thermostatic expansion valve (TXV)
D) Crankcase heater
Correct Answer: B
Rationale: A suction line accumulator is installed in the suction line
immediately before the compressor. Its primary function is to trap liquid
refrigerant and oil carried over from the evaporator, preventing liquid
from reaching the compressor cylinders where it could cause
,mechanical damage (liquid slugging). Options A, C, and D serve different
purposes.
5. When an expansion valve is operating properly, what will the state
of the refrigerant be at the end of the evaporator?
A) A mixture of liquid and vapor
B) Only superheated vapor
C) Only saturated liquid
D) Subcooled liquid
Correct Answer: B
Rationale: A properly operating expansion valve meters refrigerant so
that it is completely vaporized by the end of the evaporator coil. Any
additional heat absorbed after complete vaporization is known as
superheat. This ensures that only superheated vapor returns to the
compressor, preventing liquid slugging. Options A, C, and D are
incorrect.
6. What is the primary purpose of a purge unit on a low-pressure
centrifugal chiller?
A) To add refrigerant to the system
B) To remove non-condensables (air and moisture) from the condenser
C) To increase suction pressure
D) To provide additional cooling to the evaporator
Correct Answer: B
Rationale: Low-pressure chillers operate below atmospheric pressure,
which can allow air and moisture to leak into the system. Non-
condensables such as air accumulate in the condenser and degrade
performance by raising condensing pressure and reducing capacity. A
purge unit automatically removes these non-condensables. Options A,
C, and D are not the purpose of a purge unit.
, 7. A refrigeration system uses a jet ejector to raise settled oil mixed
with refrigerant to the oil pump. If a restriction in the refrigerant flow
to the jet ejector develops:
A) There may be insufficient head to lift the oil
B) The oil pump will overheat
C) The compressor will short-cycle
D) The evaporator will flood
Correct Answer: A
Rationale: The jet ejector uses the pressure and flow of refrigerant to
create a pumping action that lifts oil back to the oil pump or
compressor crankcase. If the refrigerant flow to the ejector is restricted,
the ejector loses its motive force, and there may be insufficient head
(pressure) to lift the oil. Options B, C, and D are not the direct
consequences of a restriction in the jet ejector's refrigerant supply.
8. What device records the speed of a turbine's shaft?
A) Thermocouple
B) Tachometer
C) Manometer
D) Ohmmeter
Correct Answer: B
Rationale: A tachometer is an instrument used to measure the rotation
speed of a shaft or disk, typically in revolutions per minute (RPM). A
thermocouple measures temperature, a manometer measures
pressure, and an ohmmeter measures electrical resistance. Options A,
C, and D are incorrect.
9. When finished leak testing with R-22 and nitrogen, what is the next
step?
A) Vent refrigerant and nitrogen to open air
EXAM QUESTIONS COMPLETE WITH 100% VERIFIED
ANSWERS
1. What is the primary function of a compressor in a vapor-
compression refrigeration system?
A) To absorb heat from the refrigerated space
B) To raise the pressure and temperature of the refrigerant vapor
C) To reject heat to the ambient air or water
D) To meter liquid refrigerant into the evaporator
Correct Answer: B
Rationale: The compressor is the "heart" of the system. Its primary
function is to draw in low-pressure, low-temperature refrigerant vapor
from the evaporator and compress it into a high-pressure, high-
temperature vapor that can be condensed in the condenser. Options A,
C, and D describe the functions of the evaporator, condenser, and
expansion device, respectively.
2. According to ASHRAE Standard 34, what do the letters and numbers
in a refrigerant safety classification (e.g., A1, B2) represent?
A) The first character represents flammability; the second represents
toxicity.
B) The first character represents toxicity; the second represents
flammability.
C) The number represents the refrigerant's ozone depletion potential.
D) The letters indicate the refrigerant's chemical family.
,Correct Answer: B
Rationale: ASHRAE Standard 34 classifies refrigerants by toxicity (Class
A = lower toxicity, Class B = higher toxicity) and flammability (Class 1 =
no flame propagation, 2L = lower flammability, 2 = moderate, 3 = high).
Option B correctly identifies this order. Option A reverses the order.
3. What is the function of a Kingsbury thrust bearing in a steam
turbine?
A) To maintain first-stage steam pressure
B) To compensate for coupling misalignment
C) To maintain the axial positioning of the rotor shaft
D) To adjust shaft torque during startup
Correct Answer: C
Rationale: The Kingsbury thrust bearing is a type of tilting-pad thrust
bearing used to absorb axial thrust loads and maintain the precise axial
positioning of the rotor shaft. It does not maintain pressure or
compensate for misalignment. Options A, B, and D are incorrect.
4. Which component in a refrigeration system is specifically designed
to prevent liquid refrigerant from entering the compressor suction
inlet during operation?
A) Liquid receiver
B) Suction line accumulator
C) Thermostatic expansion valve (TXV)
D) Crankcase heater
Correct Answer: B
Rationale: A suction line accumulator is installed in the suction line
immediately before the compressor. Its primary function is to trap liquid
refrigerant and oil carried over from the evaporator, preventing liquid
from reaching the compressor cylinders where it could cause
,mechanical damage (liquid slugging). Options A, C, and D serve different
purposes.
5. When an expansion valve is operating properly, what will the state
of the refrigerant be at the end of the evaporator?
A) A mixture of liquid and vapor
B) Only superheated vapor
C) Only saturated liquid
D) Subcooled liquid
Correct Answer: B
Rationale: A properly operating expansion valve meters refrigerant so
that it is completely vaporized by the end of the evaporator coil. Any
additional heat absorbed after complete vaporization is known as
superheat. This ensures that only superheated vapor returns to the
compressor, preventing liquid slugging. Options A, C, and D are
incorrect.
6. What is the primary purpose of a purge unit on a low-pressure
centrifugal chiller?
A) To add refrigerant to the system
B) To remove non-condensables (air and moisture) from the condenser
C) To increase suction pressure
D) To provide additional cooling to the evaporator
Correct Answer: B
Rationale: Low-pressure chillers operate below atmospheric pressure,
which can allow air and moisture to leak into the system. Non-
condensables such as air accumulate in the condenser and degrade
performance by raising condensing pressure and reducing capacity. A
purge unit automatically removes these non-condensables. Options A,
C, and D are not the purpose of a purge unit.
, 7. A refrigeration system uses a jet ejector to raise settled oil mixed
with refrigerant to the oil pump. If a restriction in the refrigerant flow
to the jet ejector develops:
A) There may be insufficient head to lift the oil
B) The oil pump will overheat
C) The compressor will short-cycle
D) The evaporator will flood
Correct Answer: A
Rationale: The jet ejector uses the pressure and flow of refrigerant to
create a pumping action that lifts oil back to the oil pump or
compressor crankcase. If the refrigerant flow to the ejector is restricted,
the ejector loses its motive force, and there may be insufficient head
(pressure) to lift the oil. Options B, C, and D are not the direct
consequences of a restriction in the jet ejector's refrigerant supply.
8. What device records the speed of a turbine's shaft?
A) Thermocouple
B) Tachometer
C) Manometer
D) Ohmmeter
Correct Answer: B
Rationale: A tachometer is an instrument used to measure the rotation
speed of a shaft or disk, typically in revolutions per minute (RPM). A
thermocouple measures temperature, a manometer measures
pressure, and an ohmmeter measures electrical resistance. Options A,
C, and D are incorrect.
9. When finished leak testing with R-22 and nitrogen, what is the next
step?
A) Vent refrigerant and nitrogen to open air
