FDNY Z51 WRITTEN EXAM 2026 NEWEST
EXAM– 350 PRACTICE QUESTIONS WITH
DETAILED RATIONALES
Section 1: Refrigeration Fundamentals & Theory
1. Which of the following best describes the primary function of a
refrigerant in a mechanical refrigeration system?
A) To absorb heat at a low temperature and reject it at a higher
temperature.
B) To generate cold directly through chemical reactions.
C) To lubricate the compressor and reduce friction.
D) To provide power to the compressor.
Correct Answer: A
Rationale: A refrigerant is a working fluid that absorbs heat from the
space to be cooled (evaporator) and transports it to another location
where it is rejected (condenser), enabling the cooling effect. Lubrication
is a separate function of oil, and power is supplied externally.
2. Sensible heat is defined as:
A) Heat that causes a change in state without a change in temperature.
B) Heat that causes a change in temperature without a change in state.
,C) Heat that is lost through the walls of a pipe.
D) Heat that is generated by the compressor.
Correct Answer: B
Rationale: Sensible heat is heat added or removed that results in a
temperature change. Latent heat, in contrast, causes a phase change at
a constant temperature.
3. Latent heat of vaporization is the heat required to:
A) Raise the temperature of a liquid by 1°F.
B) Change a substance from a solid to a liquid.
C) Change a substance from a liquid to a vapor at a constant
temperature.
D) Cool a vapor to its dew point.
Correct Answer: C
Rationale: The latent heat of vaporization is the energy absorbed when
a liquid changes into a vapor at its boiling point without a temperature
change.
4. In a refrigeration cycle, the component that separates the high-
pressure side from the low-pressure side is the:
A) Compressor.
B) Condenser.
C) Evaporator.
D) Metering device.
,Correct Answer: D
Rationale: The metering device (e.g., expansion valve) creates a
pressure drop, separating the high-pressure liquid line from the low-
pressure evaporator.
5. The evaporator in a refrigeration system is responsible for:
A) Rejecting heat to the outside air.
B) Absorbing heat from the refrigerated space.
C) Compressing the refrigerant vapor.
D) Storing liquid refrigerant.
Correct Answer: B
Rationale: The evaporator absorbs heat from the space or product being
cooled, causing the refrigerant to evaporate.
6. Subcooling the refrigerant in the condenser serves to:
A) Ensure a pure liquid refrigerant enters the metering device.
B) Increase the compressor discharge temperature.
C) Reduce the evaporator pressure.
D) Prevent the condenser from freezing.
Correct Answer: A
Rationale: Subcooling provides a margin of safety to guarantee that no
flash gas enters the metering device, improving system efficiency.
, 7. Which of the following is the correct sequence of the four basic stages
of a mechanical refrigeration cycle?
A) Evaporation → Compression → Condensation → Expansion.
B) Compression → Condensation → Expansion → Evaporation.
C) Condensation → Expansion → Evaporation → Compression.
D) Expansion → Evaporation → Compression → Condensation.
Correct Answer: B
Rationale: The standard cycle is: compression of vapor, condensation to
liquid, expansion through a metering device, and evaporation back to
vapor.
8. The pressure-enthalpy (P-H) diagram is used to:
A) Measure the physical dimensions of a compressor.
B) Analyze the thermodynamic properties and energy changes in a
refrigeration cycle.
C) Calculate the electrical resistance of a motor.
D) Determine the water flow rate in a cooling tower.
Correct Answer: B
Rationale: The P-H diagram plots pressure versus enthalpy and is a
fundamental tool for evaluating cycle performance, including work and
heat transfer.
9. Which of the following is a primary method of heat transfer that
occurs in a condenser?
A) Conduction only.
EXAM– 350 PRACTICE QUESTIONS WITH
DETAILED RATIONALES
Section 1: Refrigeration Fundamentals & Theory
1. Which of the following best describes the primary function of a
refrigerant in a mechanical refrigeration system?
A) To absorb heat at a low temperature and reject it at a higher
temperature.
B) To generate cold directly through chemical reactions.
C) To lubricate the compressor and reduce friction.
D) To provide power to the compressor.
Correct Answer: A
Rationale: A refrigerant is a working fluid that absorbs heat from the
space to be cooled (evaporator) and transports it to another location
where it is rejected (condenser), enabling the cooling effect. Lubrication
is a separate function of oil, and power is supplied externally.
2. Sensible heat is defined as:
A) Heat that causes a change in state without a change in temperature.
B) Heat that causes a change in temperature without a change in state.
,C) Heat that is lost through the walls of a pipe.
D) Heat that is generated by the compressor.
Correct Answer: B
Rationale: Sensible heat is heat added or removed that results in a
temperature change. Latent heat, in contrast, causes a phase change at
a constant temperature.
3. Latent heat of vaporization is the heat required to:
A) Raise the temperature of a liquid by 1°F.
B) Change a substance from a solid to a liquid.
C) Change a substance from a liquid to a vapor at a constant
temperature.
D) Cool a vapor to its dew point.
Correct Answer: C
Rationale: The latent heat of vaporization is the energy absorbed when
a liquid changes into a vapor at its boiling point without a temperature
change.
4. In a refrigeration cycle, the component that separates the high-
pressure side from the low-pressure side is the:
A) Compressor.
B) Condenser.
C) Evaporator.
D) Metering device.
,Correct Answer: D
Rationale: The metering device (e.g., expansion valve) creates a
pressure drop, separating the high-pressure liquid line from the low-
pressure evaporator.
5. The evaporator in a refrigeration system is responsible for:
A) Rejecting heat to the outside air.
B) Absorbing heat from the refrigerated space.
C) Compressing the refrigerant vapor.
D) Storing liquid refrigerant.
Correct Answer: B
Rationale: The evaporator absorbs heat from the space or product being
cooled, causing the refrigerant to evaporate.
6. Subcooling the refrigerant in the condenser serves to:
A) Ensure a pure liquid refrigerant enters the metering device.
B) Increase the compressor discharge temperature.
C) Reduce the evaporator pressure.
D) Prevent the condenser from freezing.
Correct Answer: A
Rationale: Subcooling provides a margin of safety to guarantee that no
flash gas enters the metering device, improving system efficiency.
, 7. Which of the following is the correct sequence of the four basic stages
of a mechanical refrigeration cycle?
A) Evaporation → Compression → Condensation → Expansion.
B) Compression → Condensation → Expansion → Evaporation.
C) Condensation → Expansion → Evaporation → Compression.
D) Expansion → Evaporation → Compression → Condensation.
Correct Answer: B
Rationale: The standard cycle is: compression of vapor, condensation to
liquid, expansion through a metering device, and evaporation back to
vapor.
8. The pressure-enthalpy (P-H) diagram is used to:
A) Measure the physical dimensions of a compressor.
B) Analyze the thermodynamic properties and energy changes in a
refrigeration cycle.
C) Calculate the electrical resistance of a motor.
D) Determine the water flow rate in a cooling tower.
Correct Answer: B
Rationale: The P-H diagram plots pressure versus enthalpy and is a
fundamental tool for evaluating cycle performance, including work and
heat transfer.
9. Which of the following is a primary method of heat transfer that
occurs in a condenser?
A) Conduction only.
