FDNY Z51 WRITTEN EXAM | ALL QUESTIONS AND
ANSWERS | EXAM PREP Q&A 2026/2027 | A+ GRADED
| COMPREHENSIVE EXAM GUIDE
1. A refrigeration compressor is operating, but the evaporator is not receiving an
adequate flow of refrigerant. Which component is most directly responsible for
regulating the amount of refrigerant entering the evaporator?
A. Condenser fan
B. Metering device
C. Receiver
D. Accumulator
Rationale: The metering device controls refrigerant flow from the high-pressure side into the
lower-pressure evaporator.
2. During normal vapor-compression refrigeration operation, where should the
refrigerant absorb heat from the space or product being cooled?
A. Condenser
B. Receiver
C. Evaporator
D. Compressor
Rationale: The evaporator is the heat-absorbing component where refrigerant boils at a low
pressure and temperature.
3. A technician observes that liquid refrigerant is returning to a reciprocating
compressor. What condition is of greatest concern?
A. Liquid slugging
B. High superheat
C. Low condensing pressure
D. Excessive subcooling
Rationale: Liquid entering a compressor can cause mechanical damage because compressors
are designed primarily to compress vapor.
4. Which component removes heat from refrigerant vapor and rejects that heat to the
surrounding environment?
A. Evaporator
B. Compressor
C. Expansion valve
D. Condenser
,Rationale: The condenser rejects heat from the refrigerant and changes high-pressure vapor
into liquid.
5. A compressor increases the pressure and temperature of refrigerant vapor before it
enters the condenser. Which process is occurring?
A. Compression
B. Condensation
C. Expansion
D. Evaporation
Rationale: The compressor raises the refrigerant vapor pressure and temperature so heat can
subsequently be rejected in the condenser.
6. A refrigeration system has unusually high suction superheat. Which condition could
contribute to this problem?
A. Excessive liquid entering the compressor
B. An overfeeding expansion valve
C. An underfeeding evaporator
D. Extremely low compressor discharge temperature
Rationale: An underfed evaporator can cause refrigerant to become fully vaporized too early,
increasing suction superheat.
7. Why is superheat important when evaluating refrigerant returning to a
compressor?
A. It confirms that the condenser contains liquid
B. It helps prevent liquid refrigerant from entering the compressor
C. It determines motor voltage
D. It measures oil viscosity
Rationale: Adequate suction superheat helps ensure the refrigerant entering the compressor is
vapor rather than liquid.
8. A condenser is heavily fouled with dirt and cannot reject heat effectively. Which
operating condition is most likely?
A. Increased condensing pressure
B. Decreased discharge pressure
C. Increased evaporator pressure only
D. Zero compressor load
Rationale: Restricted heat rejection causes condensing temperature and pressure to rise.
9. Which refrigerant property is particularly important when evaluating the safety
classification of a refrigerant?
A. Color
, B. Flammability and toxicity
C. Compressor horsepower alone
D. Pipe diameter alone
Rationale: Refrigerant safety classifications consider characteristics such as toxicity and
flammability.
10. Before servicing a refrigeration system containing refrigerant, what is the most
appropriate first consideration?
A. Increase compressor speed
B. Verify the refrigerant and applicable safety requirements
C. Close every valve immediately
D. Remove the electrical disconnect label
Rationale: Identifying the refrigerant and applicable safety requirements is essential before
selecting service procedures.
11. A refrigeration compressor repeatedly trips on high-pressure protection. Which
condition should be investigated first?
A. Dirty condenser or inadequate condenser airflow
B. Excessive evaporator airflow
C. Low suction superheat only
D. Clean condenser coils
Rationale: Poor condenser heat rejection is a common cause of elevated discharge pressure
and high-pressure trips.
12. What is the primary function of a receiver in a refrigeration system?
A. Increase suction temperature
B. Store liquid refrigerant
C. Remove compressor oil
D. Reduce motor voltage
Rationale: A receiver provides storage for liquid refrigerant and helps accommodate varying
system charge requirements.
13. A technician needs to determine whether a refrigeration system has adequate
subcooling. Where is subcooling normally evaluated?
A. Liquid leaving the condenser
B. Compressor suction inlet
C. Evaporator outlet only
D. Compressor crankcase
Rationale: Subcooling is evaluated by comparing liquid-line temperature with the saturation
temperature corresponding to the liquid pressure.
, 14. What is the primary purpose of an accumulator installed in the suction line?
A. Store excess liquid and help protect the compressor
B. Increase condenser pressure
C. Add heat to the evaporator
D. Replace the expansion device
Rationale: A suction accumulator helps prevent liquid refrigerant from reaching the
compressor.
15. A technician hears unusual knocking from a reciprocating compressor shortly after
startup. Which condition should receive immediate attention?
A. Normal superheat
B. Possible liquid slugging
C. Proper oil return
D. Normal vapor compression
Rationale: Liquid entering the compressor can produce abnormal mechanical noise and
potentially cause serious internal damage.
16. Which device is designed to remove moisture and certain contaminants from
refrigerant circulating through a system?
A. Filter-drier
B. Receiver
C. Pressure switch
D. Sight glass only
Rationale: A filter-drier removes moisture and particulate contaminants and may also capture
certain acids.
17. Why is moisture particularly undesirable inside a refrigeration system?
A. It always increases compressor horsepower efficiency
B. It can cause corrosion, freezing, and chemical reactions
C. It increases refrigerant purity
D. It eliminates the need for evacuation
Answer: B
Rationale: Moisture can freeze at metering devices, promote corrosion, and contribute to
harmful chemical reactions.
18. A refrigeration system has been opened for repair. Before charging refrigerant,
what should generally be done after the repair is completed?
A. Introduce air to test the system
B. Evacuate the system appropriately
C. Operate the compressor without refrigerant
D. Remove all service valves
ANSWERS | EXAM PREP Q&A 2026/2027 | A+ GRADED
| COMPREHENSIVE EXAM GUIDE
1. A refrigeration compressor is operating, but the evaporator is not receiving an
adequate flow of refrigerant. Which component is most directly responsible for
regulating the amount of refrigerant entering the evaporator?
A. Condenser fan
B. Metering device
C. Receiver
D. Accumulator
Rationale: The metering device controls refrigerant flow from the high-pressure side into the
lower-pressure evaporator.
2. During normal vapor-compression refrigeration operation, where should the
refrigerant absorb heat from the space or product being cooled?
A. Condenser
B. Receiver
C. Evaporator
D. Compressor
Rationale: The evaporator is the heat-absorbing component where refrigerant boils at a low
pressure and temperature.
3. A technician observes that liquid refrigerant is returning to a reciprocating
compressor. What condition is of greatest concern?
A. Liquid slugging
B. High superheat
C. Low condensing pressure
D. Excessive subcooling
Rationale: Liquid entering a compressor can cause mechanical damage because compressors
are designed primarily to compress vapor.
4. Which component removes heat from refrigerant vapor and rejects that heat to the
surrounding environment?
A. Evaporator
B. Compressor
C. Expansion valve
D. Condenser
,Rationale: The condenser rejects heat from the refrigerant and changes high-pressure vapor
into liquid.
5. A compressor increases the pressure and temperature of refrigerant vapor before it
enters the condenser. Which process is occurring?
A. Compression
B. Condensation
C. Expansion
D. Evaporation
Rationale: The compressor raises the refrigerant vapor pressure and temperature so heat can
subsequently be rejected in the condenser.
6. A refrigeration system has unusually high suction superheat. Which condition could
contribute to this problem?
A. Excessive liquid entering the compressor
B. An overfeeding expansion valve
C. An underfeeding evaporator
D. Extremely low compressor discharge temperature
Rationale: An underfed evaporator can cause refrigerant to become fully vaporized too early,
increasing suction superheat.
7. Why is superheat important when evaluating refrigerant returning to a
compressor?
A. It confirms that the condenser contains liquid
B. It helps prevent liquid refrigerant from entering the compressor
C. It determines motor voltage
D. It measures oil viscosity
Rationale: Adequate suction superheat helps ensure the refrigerant entering the compressor is
vapor rather than liquid.
8. A condenser is heavily fouled with dirt and cannot reject heat effectively. Which
operating condition is most likely?
A. Increased condensing pressure
B. Decreased discharge pressure
C. Increased evaporator pressure only
D. Zero compressor load
Rationale: Restricted heat rejection causes condensing temperature and pressure to rise.
9. Which refrigerant property is particularly important when evaluating the safety
classification of a refrigerant?
A. Color
, B. Flammability and toxicity
C. Compressor horsepower alone
D. Pipe diameter alone
Rationale: Refrigerant safety classifications consider characteristics such as toxicity and
flammability.
10. Before servicing a refrigeration system containing refrigerant, what is the most
appropriate first consideration?
A. Increase compressor speed
B. Verify the refrigerant and applicable safety requirements
C. Close every valve immediately
D. Remove the electrical disconnect label
Rationale: Identifying the refrigerant and applicable safety requirements is essential before
selecting service procedures.
11. A refrigeration compressor repeatedly trips on high-pressure protection. Which
condition should be investigated first?
A. Dirty condenser or inadequate condenser airflow
B. Excessive evaporator airflow
C. Low suction superheat only
D. Clean condenser coils
Rationale: Poor condenser heat rejection is a common cause of elevated discharge pressure
and high-pressure trips.
12. What is the primary function of a receiver in a refrigeration system?
A. Increase suction temperature
B. Store liquid refrigerant
C. Remove compressor oil
D. Reduce motor voltage
Rationale: A receiver provides storage for liquid refrigerant and helps accommodate varying
system charge requirements.
13. A technician needs to determine whether a refrigeration system has adequate
subcooling. Where is subcooling normally evaluated?
A. Liquid leaving the condenser
B. Compressor suction inlet
C. Evaporator outlet only
D. Compressor crankcase
Rationale: Subcooling is evaluated by comparing liquid-line temperature with the saturation
temperature corresponding to the liquid pressure.
, 14. What is the primary purpose of an accumulator installed in the suction line?
A. Store excess liquid and help protect the compressor
B. Increase condenser pressure
C. Add heat to the evaporator
D. Replace the expansion device
Rationale: A suction accumulator helps prevent liquid refrigerant from reaching the
compressor.
15. A technician hears unusual knocking from a reciprocating compressor shortly after
startup. Which condition should receive immediate attention?
A. Normal superheat
B. Possible liquid slugging
C. Proper oil return
D. Normal vapor compression
Rationale: Liquid entering the compressor can produce abnormal mechanical noise and
potentially cause serious internal damage.
16. Which device is designed to remove moisture and certain contaminants from
refrigerant circulating through a system?
A. Filter-drier
B. Receiver
C. Pressure switch
D. Sight glass only
Rationale: A filter-drier removes moisture and particulate contaminants and may also capture
certain acids.
17. Why is moisture particularly undesirable inside a refrigeration system?
A. It always increases compressor horsepower efficiency
B. It can cause corrosion, freezing, and chemical reactions
C. It increases refrigerant purity
D. It eliminates the need for evacuation
Answer: B
Rationale: Moisture can freeze at metering devices, promote corrosion, and contribute to
harmful chemical reactions.
18. A refrigeration system has been opened for repair. Before charging refrigerant,
what should generally be done after the repair is completed?
A. Introduce air to test the system
B. Evacuate the system appropriately
C. Operate the compressor without refrigerant
D. Remove all service valves
