FDNY Z-51 / Q-01 REFRIGERATING SYSTEM OPERATING ENGINEER - RSOE
FUNDAMENTALS — ACTUAL QUESTIONS AND VERIFIED ANSWERS — NEW
UPDATED FORMAT 2026
Question 1
A refrigeration system shows a high discharge pressure while the evaporator pressure remains near normal.
Which condition is the MOST likely starting point for investigation?
A. Insufficient condenser heat rejection
B. A failed evaporator fan only
C. An excessively low evaporating temperature
D. A completely empty receiver
CORRECT ANSWER: A. Insufficient condenser heat rejection
Explanation: High discharge pressure commonly points toward a condenser-side heat-rejection problem, such as fouling,
inadequate airflow, or insufficient cooling-water flow. The other choices do not best explain the combination.
Question 2
During a routine inspection, an operator notices that a condenser-water strainer is heavily obstructed.
What is the primary operating concern?
A. Immediate loss of all refrigerant charge
B. Reduced heat transfer and elevated condensing pressure
C. A decrease in compressor motor voltage
D. An increase in evaporator superheat caused directly by the strainer
CORRECT ANSWER: B. Reduced heat transfer and elevated condensing pressure
Explanation: A restricted condenser-water path reduces heat rejection. Condensing temperature and pressure can rise as a
result.
Question 3
Which measurement is MOST useful for determining whether a thermostatic expansion valve is feeding an
evaporator appropriately?
A. Receiver shell temperature alone
B. Compressor nameplate horsepower
C. Evaporator outlet superheat
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 1
, D. Building supply-air temperature alone
CORRECT ANSWER: C. Evaporator outlet superheat
Explanation: Superheat at the evaporator outlet helps indicate whether the metering device is supplying an appropriate amount
of refrigerant while protecting the compressor from liquid return.
Question 4
A compressor has unusually high oil temperature but normal suction pressure. Which investigation is most
appropriate?
A. Ignore it because suction pressure is normal
B. Immediately add an unlimited amount of oil
C. Close the compressor discharge valve while operating
D. Check lubrication condition, oil level, cooling, and operating conditions
CORRECT ANSWER: D. Check lubrication condition, oil level, cooling, and operating conditions
Explanation: High oil temperature can result from lubrication problems, inadequate cooling, excessive compression
temperature, or other operating issues. It warrants systematic investigation.
Question 5
Why is a liquid receiver used in many refrigeration systems?
A. To store liquid refrigerant and help accommodate charge variations
B. To replace the condenser
C. To remove all oil from the system
D. To compress vapor refrigerant
CORRECT ANSWER: A. To store liquid refrigerant and help accommodate charge variations
Explanation: A receiver provides controlled storage for liquid refrigerant and can help accommodate changes in operating
conditions and refrigerant inventory.
Question 6
A sight glass in a liquid line is intended primarily to help an operator observe what condition?
A. The thickness of pipe insulation
B. The condition of refrigerant flow in the liquid line
C. The electrical resistance of the motor
D. The compressor crankshaft speed
CORRECT ANSWER: B. The condition of refrigerant flow in the liquid line
Explanation: A liquid-line sight glass can provide useful visual information about refrigerant condition and flow, depending on its
design and application.
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 2
, Question 7
What is the main purpose of a filter-drier installed in a refrigeration liquid line?
A. To convert vapor directly into electricity
B. To increase compressor displacement
C. To remove moisture and filter contaminants
D. To regulate building occupancy
CORRECT ANSWER: C. To remove moisture and filter contaminants
Explanation: Filter-driers protect refrigeration components by removing moisture and filtering particulate contaminants from the
refrigerant circuit.
Question 8
A pressure relief device opens because pressure reaches its set point. What should the operator do first?
A. Restart repeatedly until the device closes
B. Raise the pressure set point without investigation
C. Block the relief outlet so more refrigerant cannot escape
D. Follow the system's emergency procedure and determine the cause of overpressure
CORRECT ANSWER: D. Follow the system's emergency procedure and determine the cause of overpressure
Explanation: A relief event indicates a potentially serious overpressure condition. The operator should follow established
emergency procedures and identify the cause rather than defeating the protective device.
Question 9
Which condition can cause excessive compressor discharge temperature?
A. High compression ratio or inadequate compressor cooling
B. A clean condenser operating normally
C. Correct refrigerant charge under stable load
D. Normal oil level by itself
CORRECT ANSWER: A. High compression ratio or inadequate compressor cooling
Explanation: High compression ratio, high condensing conditions, insufficient cooling, and some refrigerant or operating
problems can increase discharge temperature.
Question 10
When recovering refrigerant from equipment, why is an approved recovery method important?
A. It guarantees the compressor never needs maintenance
B. It prevents intentional venting and allows refrigerant to be handled appropriately
C. It eliminates the need for records
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 3
, D. It makes pressure readings unnecessary
CORRECT ANSWER: B. It prevents intentional venting and allows refrigerant to be handled appropriately
Explanation: Recovery procedures are designed to safely remove refrigerant for appropriate handling and to avoid intentional
release to the atmosphere.
Question 11
A compressor short-cycles repeatedly. Which item should be investigated first?
A. The building's exterior lighting
B. The receiver label font
C. Control settings, load conditions, pressure controls, and causes of rapid cycling
D. Only the paint color of the compressor
CORRECT ANSWER: C. Control settings, load conditions, pressure controls, and causes of rapid cycling
Explanation: Short cycling can be caused by control settings, inadequate system volume, load problems, or other faults. The
controls and operating conditions should be checked systematically.
Question 12
Why is a crankcase heater commonly used on certain compressors?
A. To increase condenser-water flow
B. To reduce electrical supply frequency
C. To replace the oil pump
D. To help prevent refrigerant migration and dilution of compressor oil during shutdown
CORRECT ANSWER: D. To help prevent refrigerant migration and dilution of compressor oil during shutdown
Explanation: A crankcase heater can keep oil warm enough to reduce refrigerant migration into the compressor crankcase
during shutdown.
Question 13
A refrigeration compressor is running with very low suction pressure. Which condition could produce this
symptom?
A. Restricted refrigerant flow or insufficient evaporator load
B. A properly operating liquid line with no restriction
C. A full receiver by itself
D. An oversized condenser fan alone in every case
CORRECT ANSWER: A. Restricted refrigerant flow or insufficient evaporator load
Explanation: Low suction pressure may result from insufficient refrigerant feed, restrictions, low evaporator load, or other
faults. The complete system must be evaluated.
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 4
FUNDAMENTALS — ACTUAL QUESTIONS AND VERIFIED ANSWERS — NEW
UPDATED FORMAT 2026
Question 1
A refrigeration system shows a high discharge pressure while the evaporator pressure remains near normal.
Which condition is the MOST likely starting point for investigation?
A. Insufficient condenser heat rejection
B. A failed evaporator fan only
C. An excessively low evaporating temperature
D. A completely empty receiver
CORRECT ANSWER: A. Insufficient condenser heat rejection
Explanation: High discharge pressure commonly points toward a condenser-side heat-rejection problem, such as fouling,
inadequate airflow, or insufficient cooling-water flow. The other choices do not best explain the combination.
Question 2
During a routine inspection, an operator notices that a condenser-water strainer is heavily obstructed.
What is the primary operating concern?
A. Immediate loss of all refrigerant charge
B. Reduced heat transfer and elevated condensing pressure
C. A decrease in compressor motor voltage
D. An increase in evaporator superheat caused directly by the strainer
CORRECT ANSWER: B. Reduced heat transfer and elevated condensing pressure
Explanation: A restricted condenser-water path reduces heat rejection. Condensing temperature and pressure can rise as a
result.
Question 3
Which measurement is MOST useful for determining whether a thermostatic expansion valve is feeding an
evaporator appropriately?
A. Receiver shell temperature alone
B. Compressor nameplate horsepower
C. Evaporator outlet superheat
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 1
, D. Building supply-air temperature alone
CORRECT ANSWER: C. Evaporator outlet superheat
Explanation: Superheat at the evaporator outlet helps indicate whether the metering device is supplying an appropriate amount
of refrigerant while protecting the compressor from liquid return.
Question 4
A compressor has unusually high oil temperature but normal suction pressure. Which investigation is most
appropriate?
A. Ignore it because suction pressure is normal
B. Immediately add an unlimited amount of oil
C. Close the compressor discharge valve while operating
D. Check lubrication condition, oil level, cooling, and operating conditions
CORRECT ANSWER: D. Check lubrication condition, oil level, cooling, and operating conditions
Explanation: High oil temperature can result from lubrication problems, inadequate cooling, excessive compression
temperature, or other operating issues. It warrants systematic investigation.
Question 5
Why is a liquid receiver used in many refrigeration systems?
A. To store liquid refrigerant and help accommodate charge variations
B. To replace the condenser
C. To remove all oil from the system
D. To compress vapor refrigerant
CORRECT ANSWER: A. To store liquid refrigerant and help accommodate charge variations
Explanation: A receiver provides controlled storage for liquid refrigerant and can help accommodate changes in operating
conditions and refrigerant inventory.
Question 6
A sight glass in a liquid line is intended primarily to help an operator observe what condition?
A. The thickness of pipe insulation
B. The condition of refrigerant flow in the liquid line
C. The electrical resistance of the motor
D. The compressor crankshaft speed
CORRECT ANSWER: B. The condition of refrigerant flow in the liquid line
Explanation: A liquid-line sight glass can provide useful visual information about refrigerant condition and flow, depending on its
design and application.
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 2
, Question 7
What is the main purpose of a filter-drier installed in a refrigeration liquid line?
A. To convert vapor directly into electricity
B. To increase compressor displacement
C. To remove moisture and filter contaminants
D. To regulate building occupancy
CORRECT ANSWER: C. To remove moisture and filter contaminants
Explanation: Filter-driers protect refrigeration components by removing moisture and filtering particulate contaminants from the
refrigerant circuit.
Question 8
A pressure relief device opens because pressure reaches its set point. What should the operator do first?
A. Restart repeatedly until the device closes
B. Raise the pressure set point without investigation
C. Block the relief outlet so more refrigerant cannot escape
D. Follow the system's emergency procedure and determine the cause of overpressure
CORRECT ANSWER: D. Follow the system's emergency procedure and determine the cause of overpressure
Explanation: A relief event indicates a potentially serious overpressure condition. The operator should follow established
emergency procedures and identify the cause rather than defeating the protective device.
Question 9
Which condition can cause excessive compressor discharge temperature?
A. High compression ratio or inadequate compressor cooling
B. A clean condenser operating normally
C. Correct refrigerant charge under stable load
D. Normal oil level by itself
CORRECT ANSWER: A. High compression ratio or inadequate compressor cooling
Explanation: High compression ratio, high condensing conditions, insufficient cooling, and some refrigerant or operating
problems can increase discharge temperature.
Question 10
When recovering refrigerant from equipment, why is an approved recovery method important?
A. It guarantees the compressor never needs maintenance
B. It prevents intentional venting and allows refrigerant to be handled appropriately
C. It eliminates the need for records
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 3
, D. It makes pressure readings unnecessary
CORRECT ANSWER: B. It prevents intentional venting and allows refrigerant to be handled appropriately
Explanation: Recovery procedures are designed to safely remove refrigerant for appropriate handling and to avoid intentional
release to the atmosphere.
Question 11
A compressor short-cycles repeatedly. Which item should be investigated first?
A. The building's exterior lighting
B. The receiver label font
C. Control settings, load conditions, pressure controls, and causes of rapid cycling
D. Only the paint color of the compressor
CORRECT ANSWER: C. Control settings, load conditions, pressure controls, and causes of rapid cycling
Explanation: Short cycling can be caused by control settings, inadequate system volume, load problems, or other faults. The
controls and operating conditions should be checked systematically.
Question 12
Why is a crankcase heater commonly used on certain compressors?
A. To increase condenser-water flow
B. To reduce electrical supply frequency
C. To replace the oil pump
D. To help prevent refrigerant migration and dilution of compressor oil during shutdown
CORRECT ANSWER: D. To help prevent refrigerant migration and dilution of compressor oil during shutdown
Explanation: A crankcase heater can keep oil warm enough to reduce refrigerant migration into the compressor crankcase
during shutdown.
Question 13
A refrigeration compressor is running with very low suction pressure. Which condition could produce this
symptom?
A. Restricted refrigerant flow or insufficient evaporator load
B. A properly operating liquid line with no restriction
C. A full receiver by itself
D. An oversized condenser fan alone in every case
CORRECT ANSWER: A. Restricted refrigerant flow or insufficient evaporator load
Explanation: Low suction pressure may result from insufficient refrigerant feed, restrictions, low evaporator load, or other
faults. The complete system must be evaluated.
FDNY Z-51 / Q-01 — ORIGINAL 2026 PRACTICE EXAM — VERSION 3 Page 4
