Z-51 EXAM STUDY GUIDE 2025/2026 QUESTIONS WITH
ANSWERS GRADED A+
✔A refrigeration engineer is logging reading from a reciprocating system. compressor
discharge temperature have dropped significantly and the suction line pressure is high.
which of the following that may be causing this set of condition. - ✔✔An expansion
valve that is open to wide
✔✔A low side float valve is used to maintain: - ✔✔The level of the refrigerant in the
evaporator
✔✔Regarding fire safety, which ASHARE refrigerant safety classification indicates no
flammability and lower the toxicity? - ✔✔A1
✔✔When an expansion valve is operating properly, at the end of the evaporator will
contain: - ✔✔Only superheated vapor
✔✔What information is not contained in a material safety data sheet-MSDS? - ✔✔Cost
of material
✔✔In a steam turbine, what is the function of the kingsbury thrust bearing - ✔✔Maintain
axial positioning of the rotor shaft
✔✔A centrifugal water pump is considered to be fully primed when - ✔✔The pump is full
of liquid
✔✔Copper tubing refrigerant lines must be installed for a new system. it is a well known
service practice that tubing collapses at bends that must be made, the refrigerant
engineer should use - ✔✔Lever type tubing bender
✔✔A reciprocating compressor is making a knocking sound during operation. if the
refrigerant worn parts are not causing the knocking, what is probably the cause -
✔✔The slugging of the liquid refrigerant
✔✔In order for a refrigerant to become superheated in a section of the lowside
refrigerant line: - ✔✔Where no liquid refrigerant is present
✔✔All liquid has been recovered from a system to be overhauled, the system -
✔✔Should not be opened until all vapor has been removed
✔✔When a refrigerant engineer uses a portable compressor recovery unit to remove
vapor refrigerant from a refrigeration system the removal rate of the refrigerant will
gradually slow down because - ✔✔The vapor density is decreasing
,✔✔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. During the course of making your rounds, you check the 9 cell
cooling tower on the roof. You note the water level in all of the cooling tower cells is very
low. Which one of the following immediate action would take? - ✔✔Add additional make
up water to cooling tower
✔✔A rooftop water cooling tower is connected to a water pump in the building
basement with a 12 inches diameter pipe. with the pump turn off, a pressure gauge at
the pumps inlet show a pressure of 140 PSIG the height of the water column, in feet,
would be closet to. - ✔✔323
✔✔What device protects the steam turbine from excessive speed? - ✔✔governor
assembly
✔✔A refrigeration compressor has failed to turn on. the refrigeration engineer on duty
verifies that the electrical circuit to the motor, including all switches and circuit breakers,
is complete according to recommended service practice, the next item to be checked
would likely be the: - ✔✔Temperature and pressure controls
✔✔Refrigerants are characterized by their physical properties included flash point,
refrigeration effect, and others. of the refrigerant in commercial and industrial the
highest latent hear and refrigerant effect is: - ✔✔Ammonia
✔✔On what characteristics is ASHRAE refrigerant safety group classification system: -
✔✔Flammability and toxicity
✔✔Of the following, and example of an in-line refrigerant cleaning system that may be
used with a centrifugal compressor containing R123 refrigerant is: - ✔✔Refrigerant
recycling
✔✔Information about the physical and chemical properties of a hazardous material can
be found in: - ✔✔Material Safety Data Sheet
✔✔What is the function of the turbine auxiliary oil pump? - ✔✔Establish oil pressure
during turbine start up
✔✔The rupture disc for a low-pressure centrifugal refrigeration machine is normally
located on the: - ✔✔Compressor suction
, ✔✔What is the primary reason ribbed metal piping is used for electrical wires connected
to the refrigeration system shown below? - ✔✔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? -
✔✔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? - ✔✔440
✔✔A water chilling system uses refrigerant R123. a leak in the evaporator shell mat
result in - ✔✔A higher than normal high side pressure
✔✔Capacitors are used on refrigeration motors. of the following, the function of these
devices is to? - ✔✔Store electrical charges during starting and running the motor
✔✔Of the following, centrifugal refrigerant machine is best characterized by: - ✔✔High
volume low pressure machine
✔✔Which of the following ASHRAE refrigerant safety classification is the most
flammable? - ✔✔A3
✔✔Which of the following correctly describes the object in the picture below? -
✔✔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 - ✔✔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: -
✔✔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: - ✔✔1099
✔✔An electrically operated control requires 24 volts to operate. to change the available
110 volts to 24 volts - ✔✔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: - ✔✔R22 refrigerant
ANSWERS GRADED A+
✔A refrigeration engineer is logging reading from a reciprocating system. compressor
discharge temperature have dropped significantly and the suction line pressure is high.
which of the following that may be causing this set of condition. - ✔✔An expansion
valve that is open to wide
✔✔A low side float valve is used to maintain: - ✔✔The level of the refrigerant in the
evaporator
✔✔Regarding fire safety, which ASHARE refrigerant safety classification indicates no
flammability and lower the toxicity? - ✔✔A1
✔✔When an expansion valve is operating properly, at the end of the evaporator will
contain: - ✔✔Only superheated vapor
✔✔What information is not contained in a material safety data sheet-MSDS? - ✔✔Cost
of material
✔✔In a steam turbine, what is the function of the kingsbury thrust bearing - ✔✔Maintain
axial positioning of the rotor shaft
✔✔A centrifugal water pump is considered to be fully primed when - ✔✔The pump is full
of liquid
✔✔Copper tubing refrigerant lines must be installed for a new system. it is a well known
service practice that tubing collapses at bends that must be made, the refrigerant
engineer should use - ✔✔Lever type tubing bender
✔✔A reciprocating compressor is making a knocking sound during operation. if the
refrigerant worn parts are not causing the knocking, what is probably the cause -
✔✔The slugging of the liquid refrigerant
✔✔In order for a refrigerant to become superheated in a section of the lowside
refrigerant line: - ✔✔Where no liquid refrigerant is present
✔✔All liquid has been recovered from a system to be overhauled, the system -
✔✔Should not be opened until all vapor has been removed
✔✔When a refrigerant engineer uses a portable compressor recovery unit to remove
vapor refrigerant from a refrigeration system the removal rate of the refrigerant will
gradually slow down because - ✔✔The vapor density is decreasing
,✔✔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. During the course of making your rounds, you check the 9 cell
cooling tower on the roof. You note the water level in all of the cooling tower cells is very
low. Which one of the following immediate action would take? - ✔✔Add additional make
up water to cooling tower
✔✔A rooftop water cooling tower is connected to a water pump in the building
basement with a 12 inches diameter pipe. with the pump turn off, a pressure gauge at
the pumps inlet show a pressure of 140 PSIG the height of the water column, in feet,
would be closet to. - ✔✔323
✔✔What device protects the steam turbine from excessive speed? - ✔✔governor
assembly
✔✔A refrigeration compressor has failed to turn on. the refrigeration engineer on duty
verifies that the electrical circuit to the motor, including all switches and circuit breakers,
is complete according to recommended service practice, the next item to be checked
would likely be the: - ✔✔Temperature and pressure controls
✔✔Refrigerants are characterized by their physical properties included flash point,
refrigeration effect, and others. of the refrigerant in commercial and industrial the
highest latent hear and refrigerant effect is: - ✔✔Ammonia
✔✔On what characteristics is ASHRAE refrigerant safety group classification system: -
✔✔Flammability and toxicity
✔✔Of the following, and example of an in-line refrigerant cleaning system that may be
used with a centrifugal compressor containing R123 refrigerant is: - ✔✔Refrigerant
recycling
✔✔Information about the physical and chemical properties of a hazardous material can
be found in: - ✔✔Material Safety Data Sheet
✔✔What is the function of the turbine auxiliary oil pump? - ✔✔Establish oil pressure
during turbine start up
✔✔The rupture disc for a low-pressure centrifugal refrigeration machine is normally
located on the: - ✔✔Compressor suction
, ✔✔What is the primary reason ribbed metal piping is used for electrical wires connected
to the refrigeration system shown below? - ✔✔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? -
✔✔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? - ✔✔440
✔✔A water chilling system uses refrigerant R123. a leak in the evaporator shell mat
result in - ✔✔A higher than normal high side pressure
✔✔Capacitors are used on refrigeration motors. of the following, the function of these
devices is to? - ✔✔Store electrical charges during starting and running the motor
✔✔Of the following, centrifugal refrigerant machine is best characterized by: - ✔✔High
volume low pressure machine
✔✔Which of the following ASHRAE refrigerant safety classification is the most
flammable? - ✔✔A3
✔✔Which of the following correctly describes the object in the picture below? -
✔✔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 - ✔✔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: -
✔✔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: - ✔✔1099
✔✔An electrically operated control requires 24 volts to operate. to change the available
110 volts to 24 volts - ✔✔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: - ✔✔R22 refrigerant
