REFRIGERATING SYSTEM OPERATING ENGINEER
FDNY Z51 ACTUAL EXAM 2026/2027 WITH
QUESTIONS AND CORRECT ANSWERS
(100% CORRECT VERIFIED ANSWERS) A+
ACTUAL FDNY Z-51 WRITTEN EXAM
(BRAND NEW!!)
Certificate of Qualification for Refrigerating System Operating Engineer (Q-01)
A+ QUESTIONS SECTIONS 100%
VERIFIED 5 RATIONALES
CATEGORIES
1. Refrigeration Fundamentals, Compressors & Components
2. Refrigerants, Safety Classifications & A2L Requirements
3. Plant Operations, Pumps, Electrical & Controls
4. NYC Fire Code, Building Code & Supervision Requirements
5. Fire Safety, BOMR, Maintenance & Emergency Procedures
STUVIAACTUALEXAM
, FDNY Z-51 Exam 2026/2027 Page 2
SECTION 1: Refrigeration Fundamentals, Compressors & Components
Q1. A centrifugal compressor in a large water-cooled chiller is operating with low suction pressure and high discharge pressure. The
operator notes that the condenser approach temperature has increased significantly. Which component problem is most consistent with
these readings?
A. A fully open expansion valve flooding the evaporator
B. Fouled or scaled condenser tubes reducing heat-transfer efficiency and elevating discharge pressure
C. Excess refrigerant charge only in the low side
D. A failed oil heater with no other effects
Correct Answer: B
Rationale: Elevated condenser approach with high discharge and low suction pressure is classic for reduced condenser heat-transfer capability from
fouling or scale.
Q2. In a reciprocating compressor, the purpose of the suction and discharge valves is to control the flow of refrigerant vapor. What
happens if a discharge valve fails to seat properly?
A. The compressor will immediately seize and stop rotating
B. Only the oil pressure will drop with no effect on capacity
C. The system will automatically pump down and shut off
D. High-pressure vapor can leak back into the cylinder, reducing volumetric efficiency and elevating suction pressure or discharge temperature
Correct Answer: D
Rationale: A leaking discharge valve allows high-pressure gas to re-enter the cylinder, cutting capacity and raising temperatures.
Q3. A shell-and-tube evaporator is used in a flooded chiller. What is the primary function of the refrigerant-side float valve or level control?
A. Maintain the correct liquid-refrigerant level so that the tubes remain wetted for efficient heat transfer without flooding the suction line
B. Control condenser water flow rate only
C. Regulate oil return to the compressor crankcase exclusively
D. Set the chilled-water leaving temperature setpoint
Correct Answer: A
Rationale: Flooded evaporators rely on level control to keep tubes submerged for heat transfer while preventing liquid carryover to the compressor.
Q4. An expansion device meters refrigerant into the evaporator. In a thermostatic expansion valve (TXV) system, what does the sensing
bulb primarily respond to?
A. Absolute condenser pressure only
B. Superheat at the evaporator outlet; the valve opens or closes to maintain the design superheat
C. Oil temperature in the compressor sump
D. Ambient outdoor air temperature exclusively
Correct Answer: B
Rationale: The TXV sensing bulb measures evaporator-outlet superheat and modulates valve opening to maintain the design superheat value.
Q5. A cooling tower supplies condenser water to a water-cooled chiller. Approach temperature is defined as the difference between which
two temperatures?
A. Chilled-water supply and return only
B. Compressor discharge and suction temperature only
C. Oil temperature and ambient dry-bulb only
D. Leaving condenser-water temperature and entering outdoor wet-bulb temperature (or the difference between leaving process water and
ambient wet bulb, depending on definition used)
Correct Answer: D
Rationale: Cooling-tower approach is commonly the difference between leaving water temperature and ambient wet-bulb temperature.
Q6. A positive-displacement compressor is protected by a high-pressure cut-out. Under normal design conditions, where should this
safety control be set relative to the system working pressure?
A. At a pressure that protects the equipment but is below the relief-device setting, typically in accordance with manufacturer and code
requirements
B. Exactly equal to the rupture-disk rating with no margin
C. Far above the relief-valve setting so it never trips
D. Only on the low-pressure side of the system
Correct Answer: A
Rationale: High-pressure cut-outs are set to protect equipment at a pressure below the relief-device setting per manufacturer and code guidance.
STUVIAACTUALEXAM
FDNY Z51 ACTUAL EXAM 2026/2027 WITH
QUESTIONS AND CORRECT ANSWERS
(100% CORRECT VERIFIED ANSWERS) A+
ACTUAL FDNY Z-51 WRITTEN EXAM
(BRAND NEW!!)
Certificate of Qualification for Refrigerating System Operating Engineer (Q-01)
A+ QUESTIONS SECTIONS 100%
VERIFIED 5 RATIONALES
CATEGORIES
1. Refrigeration Fundamentals, Compressors & Components
2. Refrigerants, Safety Classifications & A2L Requirements
3. Plant Operations, Pumps, Electrical & Controls
4. NYC Fire Code, Building Code & Supervision Requirements
5. Fire Safety, BOMR, Maintenance & Emergency Procedures
STUVIAACTUALEXAM
, FDNY Z-51 Exam 2026/2027 Page 2
SECTION 1: Refrigeration Fundamentals, Compressors & Components
Q1. A centrifugal compressor in a large water-cooled chiller is operating with low suction pressure and high discharge pressure. The
operator notes that the condenser approach temperature has increased significantly. Which component problem is most consistent with
these readings?
A. A fully open expansion valve flooding the evaporator
B. Fouled or scaled condenser tubes reducing heat-transfer efficiency and elevating discharge pressure
C. Excess refrigerant charge only in the low side
D. A failed oil heater with no other effects
Correct Answer: B
Rationale: Elevated condenser approach with high discharge and low suction pressure is classic for reduced condenser heat-transfer capability from
fouling or scale.
Q2. In a reciprocating compressor, the purpose of the suction and discharge valves is to control the flow of refrigerant vapor. What
happens if a discharge valve fails to seat properly?
A. The compressor will immediately seize and stop rotating
B. Only the oil pressure will drop with no effect on capacity
C. The system will automatically pump down and shut off
D. High-pressure vapor can leak back into the cylinder, reducing volumetric efficiency and elevating suction pressure or discharge temperature
Correct Answer: D
Rationale: A leaking discharge valve allows high-pressure gas to re-enter the cylinder, cutting capacity and raising temperatures.
Q3. A shell-and-tube evaporator is used in a flooded chiller. What is the primary function of the refrigerant-side float valve or level control?
A. Maintain the correct liquid-refrigerant level so that the tubes remain wetted for efficient heat transfer without flooding the suction line
B. Control condenser water flow rate only
C. Regulate oil return to the compressor crankcase exclusively
D. Set the chilled-water leaving temperature setpoint
Correct Answer: A
Rationale: Flooded evaporators rely on level control to keep tubes submerged for heat transfer while preventing liquid carryover to the compressor.
Q4. An expansion device meters refrigerant into the evaporator. In a thermostatic expansion valve (TXV) system, what does the sensing
bulb primarily respond to?
A. Absolute condenser pressure only
B. Superheat at the evaporator outlet; the valve opens or closes to maintain the design superheat
C. Oil temperature in the compressor sump
D. Ambient outdoor air temperature exclusively
Correct Answer: B
Rationale: The TXV sensing bulb measures evaporator-outlet superheat and modulates valve opening to maintain the design superheat value.
Q5. A cooling tower supplies condenser water to a water-cooled chiller. Approach temperature is defined as the difference between which
two temperatures?
A. Chilled-water supply and return only
B. Compressor discharge and suction temperature only
C. Oil temperature and ambient dry-bulb only
D. Leaving condenser-water temperature and entering outdoor wet-bulb temperature (or the difference between leaving process water and
ambient wet bulb, depending on definition used)
Correct Answer: D
Rationale: Cooling-tower approach is commonly the difference between leaving water temperature and ambient wet-bulb temperature.
Q6. A positive-displacement compressor is protected by a high-pressure cut-out. Under normal design conditions, where should this
safety control be set relative to the system working pressure?
A. At a pressure that protects the equipment but is below the relief-device setting, typically in accordance with manufacturer and code
requirements
B. Exactly equal to the rupture-disk rating with no margin
C. Far above the relief-valve setting so it never trips
D. Only on the low-pressure side of the system
Correct Answer: A
Rationale: High-pressure cut-outs are set to protect equipment at a pressure below the relief-device setting per manufacturer and code guidance.
STUVIAACTUALEXAM
