FDNY Z51/ written z51 Test Exam Recent 2024-
2026Version Updated with All 220 Questions and detailed
answers graded A+
What is the primary reason ribbed metal piping is used for electrical wires connected to
the refrigeration system shown below? - CORRECT ANSWER✔✔It allows for flexibility
and accounts for vibrations
A multi-cylinder reciprocating compressor uses cylinder unloaders to regulate capacity,
what would not occur if some of the unloaders fail to operate when needed? -
CORRECT ANSWER✔✔The chill water temperature will increase
As shown in the picture below, the suction gauge of a condenser water pump reads 55
PSI. the pipe supplying the pump is 75 feet long and 12 inches in diameter.
approximately how many gallons of water do you expect to obtain if this pipe is drained
completely? - CORRECT ANSWER✔✔440
A water chilling system uses refrigerant R123. a leak in the evaporator shell mat result
in - CORRECT ANSWER✔✔A higher than normal high side pressure
Capacitors are used on refrigeration motors. of the following, the function of these
devices is to? - CORRECT ANSWER✔✔Store electrical charges during starting and
running the motor
Of the following, centrifugal refrigerant machine is best characterized by: - CORRECT
ANSWER✔✔High volume low pressure machine
Which of the following ASHRAE refrigerant safety classification is the most flammable?
- CORRECT ANSWER✔✔A3
Which of the following correctly describes the object in the picture below? - CORRECT
ANSWER✔✔Standpipe hose outlet to put out fires in cae of emergency
Modern compressors usually seal the rotating shaft as it exits the compressor housing a
spring loaded seal made of - CORRECT ANSWER✔✔Metal or carbon
The British Thermal Unit (BTU) is the measurement of heat of energy. if 10 BTU are
transferred to 10 pounds of water, the water temperature increase will be closest to: -
CORRECT ANSWER✔✔1F
A reciprocating compressor cylinder has a 10 inch bore and 14 inches stroke. the
volume of refrigerant, in a cubic inches, will be closer to: - CORRECT ANSWER✔✔
1099
,An electrically operated control requires 24 volts to operate. to change the available 110
volts to 24 volts - CORRECT ANSWER✔✔Transformer
In an indirect refrigerant system, of the following , the one that would not be used as a
cooling medium for the building spaces being cooled is: - CORRECT ANSWER✔✔R22
refrigerant
On a steam turbine, what would cause the atmospheric valve to open? - CORRECT
ANSWER✔✔low vacuum in the surface condenser, leaking tubes in the surface
condenser, dirty tubes n the surface condenser
You are the engineer running a 2000-ton (steam-driven turbine) centrifugal refrigeration
system, a refrigeration system supplies chilled water to a college campus with multiple
buildings. making your rounds, you notice that condenser water pump #1 is making a lot
of noise, the discharger gauge reading of the condenser water pump is fluctuating
drastically, and motor of the condenser pump #1 is running very hot. which of the
following actions would you take: - CORRECT ANSWER✔✔Turn on pump #2 shut off
pump #1, and trouble shot pump #1
Electric devices may be used to provide built in defrosting of refrigeration machine
evaporator units. these devices are classified as - CORRECT ANSWER✔✔Resistors
The flash point of compressor lubricating oil: - CORRECT ANSWER✔✔Should be
higher than the compression temperature
The primary way of achieving capacity control of a centrifugal compressor is by; -
CORRECT ANSWER✔✔Adjustment of the impeller inlet pre-rotation vanes
Cooling tower water requires the addition of chemical additives in order to: - CORRECT
ANSWER✔✔Reduce the formation of scale and algae
In the picture below describe the equipment's function? - CORRECT ANSWER✔✔
Remove non condensable from the condenser
the viscosity of lubrication oil is described by a number. a low viscosity number
describes oil that: - CORRECT ANSWER✔✔Flows easily
The most likely reason for a refrigeration engineer to use a psychrometer is to measure
- CORRECT ANSWER✔✔Relative humidity level of the atmosphere
The most important reason to use at least two compressors in a cascade system is to: -
CORRECT ANSWER✔✔Avoid very high compression ratio for each compressor
, The suction service valve of a reciprocating compressor is front seated and the
compressor runs until the low pressure cut-out shut the compressor off. when the
machine is stopped, the refrigeration engineer notices that the suction pressure
increase rapidly. the most probable cause of this pressure rise: - CORRECT ANSWER
✔✔Malfunction of a compressor valve
Regarding the functioning of a steam turbine, why is it advisable to keep moisture in the
inlet low as possible? - CORRECT ANSWER✔✔Keeps turbine blades wear to
minimum
According to the attached Material Safety Data Sheet (MSDS) R134 is a - CORRECT
ANSWER✔✔Clear, odorless liquid and vapor
Under normal condition, the refrigerant enters the compressor as a: - CORRECT
ANSWER✔✔Low pressure superheated vapor and leaves as a high pressure vapor
While operating an R-22 single acting compressor system, the refrigeration engineer
noticed oil foaming in the crankcase. this condition most likely, would have been caused
by a : - CORRECT ANSWER✔✔Sudden drop in the crankcase pressure
Assume that an engineer is able to observe refrigerant water and oil together. the fluids
would settle in the container from top to bottom: - CORRECT ANSWER✔✔Oil, water,
refrigerant
What is the function of the vacuum breaker in a steam turbine. - CORRECT ANSWER
✔✔To achieve a faster coast down cycle
An equalizer line on a TXV is used to: - CORRECT ANSWER✔✔Compensate for the
pressure drop across the evaporator coil
If R134 accidentally touches a refrigerant engineer's skin, what first aid should be
applied from the MSDS? - CORRECT ANSWER✔✔Promptly flush skin with water until
all chemical is removed
In a multi stage centrifugal compressor, each stage: - CORRECT ANSWER✔✔Is
identical in volume to the other stages
A refrigeration engineer notices excessive cycling of the temperature control for a
reciprocating compressor refrigeration unit. the crankcase temperature is high, the
compressor discharge temperature low, the suction line temperature high. of the
following the one that may causing this set condition. - CORRECT ANSWER✔✔Faulty
compressor valves
On an operating centrifugal compressor refrigerant unit, the refrigeration engineer
notices that the compressor is short cycling. the unit is using low side float valve as a
2026Version Updated with All 220 Questions and detailed
answers graded A+
What is the primary reason ribbed metal piping is used for electrical wires connected to
the refrigeration system shown below? - CORRECT ANSWER✔✔It allows for flexibility
and accounts for vibrations
A multi-cylinder reciprocating compressor uses cylinder unloaders to regulate capacity,
what would not occur if some of the unloaders fail to operate when needed? -
CORRECT ANSWER✔✔The chill water temperature will increase
As shown in the picture below, the suction gauge of a condenser water pump reads 55
PSI. the pipe supplying the pump is 75 feet long and 12 inches in diameter.
approximately how many gallons of water do you expect to obtain if this pipe is drained
completely? - CORRECT ANSWER✔✔440
A water chilling system uses refrigerant R123. a leak in the evaporator shell mat result
in - CORRECT ANSWER✔✔A higher than normal high side pressure
Capacitors are used on refrigeration motors. of the following, the function of these
devices is to? - CORRECT ANSWER✔✔Store electrical charges during starting and
running the motor
Of the following, centrifugal refrigerant machine is best characterized by: - CORRECT
ANSWER✔✔High volume low pressure machine
Which of the following ASHRAE refrigerant safety classification is the most flammable?
- CORRECT ANSWER✔✔A3
Which of the following correctly describes the object in the picture below? - CORRECT
ANSWER✔✔Standpipe hose outlet to put out fires in cae of emergency
Modern compressors usually seal the rotating shaft as it exits the compressor housing a
spring loaded seal made of - CORRECT ANSWER✔✔Metal or carbon
The British Thermal Unit (BTU) is the measurement of heat of energy. if 10 BTU are
transferred to 10 pounds of water, the water temperature increase will be closest to: -
CORRECT ANSWER✔✔1F
A reciprocating compressor cylinder has a 10 inch bore and 14 inches stroke. the
volume of refrigerant, in a cubic inches, will be closer to: - CORRECT ANSWER✔✔
1099
,An electrically operated control requires 24 volts to operate. to change the available 110
volts to 24 volts - CORRECT ANSWER✔✔Transformer
In an indirect refrigerant system, of the following , the one that would not be used as a
cooling medium for the building spaces being cooled is: - CORRECT ANSWER✔✔R22
refrigerant
On a steam turbine, what would cause the atmospheric valve to open? - CORRECT
ANSWER✔✔low vacuum in the surface condenser, leaking tubes in the surface
condenser, dirty tubes n the surface condenser
You are the engineer running a 2000-ton (steam-driven turbine) centrifugal refrigeration
system, a refrigeration system supplies chilled water to a college campus with multiple
buildings. making your rounds, you notice that condenser water pump #1 is making a lot
of noise, the discharger gauge reading of the condenser water pump is fluctuating
drastically, and motor of the condenser pump #1 is running very hot. which of the
following actions would you take: - CORRECT ANSWER✔✔Turn on pump #2 shut off
pump #1, and trouble shot pump #1
Electric devices may be used to provide built in defrosting of refrigeration machine
evaporator units. these devices are classified as - CORRECT ANSWER✔✔Resistors
The flash point of compressor lubricating oil: - CORRECT ANSWER✔✔Should be
higher than the compression temperature
The primary way of achieving capacity control of a centrifugal compressor is by; -
CORRECT ANSWER✔✔Adjustment of the impeller inlet pre-rotation vanes
Cooling tower water requires the addition of chemical additives in order to: - CORRECT
ANSWER✔✔Reduce the formation of scale and algae
In the picture below describe the equipment's function? - CORRECT ANSWER✔✔
Remove non condensable from the condenser
the viscosity of lubrication oil is described by a number. a low viscosity number
describes oil that: - CORRECT ANSWER✔✔Flows easily
The most likely reason for a refrigeration engineer to use a psychrometer is to measure
- CORRECT ANSWER✔✔Relative humidity level of the atmosphere
The most important reason to use at least two compressors in a cascade system is to: -
CORRECT ANSWER✔✔Avoid very high compression ratio for each compressor
, The suction service valve of a reciprocating compressor is front seated and the
compressor runs until the low pressure cut-out shut the compressor off. when the
machine is stopped, the refrigeration engineer notices that the suction pressure
increase rapidly. the most probable cause of this pressure rise: - CORRECT ANSWER
✔✔Malfunction of a compressor valve
Regarding the functioning of a steam turbine, why is it advisable to keep moisture in the
inlet low as possible? - CORRECT ANSWER✔✔Keeps turbine blades wear to
minimum
According to the attached Material Safety Data Sheet (MSDS) R134 is a - CORRECT
ANSWER✔✔Clear, odorless liquid and vapor
Under normal condition, the refrigerant enters the compressor as a: - CORRECT
ANSWER✔✔Low pressure superheated vapor and leaves as a high pressure vapor
While operating an R-22 single acting compressor system, the refrigeration engineer
noticed oil foaming in the crankcase. this condition most likely, would have been caused
by a : - CORRECT ANSWER✔✔Sudden drop in the crankcase pressure
Assume that an engineer is able to observe refrigerant water and oil together. the fluids
would settle in the container from top to bottom: - CORRECT ANSWER✔✔Oil, water,
refrigerant
What is the function of the vacuum breaker in a steam turbine. - CORRECT ANSWER
✔✔To achieve a faster coast down cycle
An equalizer line on a TXV is used to: - CORRECT ANSWER✔✔Compensate for the
pressure drop across the evaporator coil
If R134 accidentally touches a refrigerant engineer's skin, what first aid should be
applied from the MSDS? - CORRECT ANSWER✔✔Promptly flush skin with water until
all chemical is removed
In a multi stage centrifugal compressor, each stage: - CORRECT ANSWER✔✔Is
identical in volume to the other stages
A refrigeration engineer notices excessive cycling of the temperature control for a
reciprocating compressor refrigeration unit. the crankcase temperature is high, the
compressor discharge temperature low, the suction line temperature high. of the
following the one that may causing this set condition. - CORRECT ANSWER✔✔Faulty
compressor valves
On an operating centrifugal compressor refrigerant unit, the refrigeration engineer
notices that the compressor is short cycling. the unit is using low side float valve as a
