1|Page
FDNY Z51 EXAM 2 NEWEST 2025 ACTUAL EXAM|
COMPLETE 400 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
ALREADY GRADED A+|FDNY Z51 WRITTEN
ACTUAL EXAM 2 |BRAND NEW!!
Which side of the compressor is R-22 vapor charged into? - ANSWER -
The suction side.
What should the percentage of lubricant circulated through a well-
designed system be? - ANSWER - Lubricant should not exceed 10%.
What is oil foaming in the compressor a result of? - ANSWER - Liquid
refrigerant in the crankcase.
What is the main reason for installing an oil separator on the discharge
line? - ANSWER - To return oil back to the compressor crank case.
What causes the foaming of oil in a reciprocating compressor using the
splash system for lubrication? - ANSWER - A rapid decrease in
pressure.
What is the purpose of oil in a refrigerant compressor? - ANSWER - It
reduces ware and friction.
pg. 1
,2|Page
What is a filter dryer used to remove? - ANSWER - Moisture, particles
and contaminants.
Where in a refrigeration system is the oil separator located? - ANSWER
- On the discharge line as far from the compressor as possible.
What accessory meters and controls the flow of refrigerant into the
evaporator? - ANSWER - The TEV (Metering Device).
What will occur if you use an automatic expansion valve with a variable
load? - ANSWER - You will starve the evaporator.
What does an automatic expansion valve do? - ANSWER - It maintains
a constant evaporator pressure.
What could cause the evaporator to not respond to the adjustments of the
TEV? - ANSWER - Oil logged on the low side.
What can non-condensable cause? - ANSWER - High head pressure.
When will compressor motor horsepower increase? - ANSWER - It will
increase as the head pressure increases.
When will compressor motor horsepower decrease? - ANSWER - As the
suction pressure increases.
pg. 2
,3|Page
When using a brine solution in a system what can be used to prevent
rusting? - ANSWER - Di-Chromate Tablets.
What would cause a Halide torch flame to turn yellow? - ANSWER - A
clogged sample tube.
What is the purpose of having 2 compressors in a cascade system? -
ANSWER - To operate and very low temperatures and avoid high
compression ratio.
Why is a pressure relief valve better than a fusible plug? - ANSWER -
Because it can be re-seated and is cost efficient.
What could cause compressor knocking? - ANSWER - Liquid
refrigerant slugging the compressor.
What would occur if a TEV'S spring were to break? - ANSWER - It
would flood the evaporator and raise the suction pressure because a TEV
uses spring pressure as its closing force. Thus, if the spring does not
close the TEV refrigerant will constantly be metered into the evaporator.
What is the purpose of the TEV equalizer line? - ANSWER - It
compensates for the pressure drop in the evaporator. Simply put, it
equalizes pressure drop lost across the evaporator.
pg. 3
, 4|Page
What should be done when installing copper pipe and a 90-degree elbow
is needed? - ANSWER - You should BRAZE in a FACTORY MADE
90-degree elbow.
What is the purpose of a service valve stem cap? - ANSWER - It
protects the valve from refrigerant leakage.
What advantage do semi hermetic compressors have over hermetic
compressor's? - ANSWER - Semi hermetic compressors can be serviced.
What happens when using portable compressor recovery unit to remove
vapor? - ANSWER - The vapor density is decreased.
What is the purpose of an unloader? - ANSWER - To decrease capacity
(capacity control).
What determines the amount of pressure that flows through the orifice
plates? - ANSWER - The difference in pressure between the high side
and the low side of the system.
How can you check proper operation of a thermometer? - ANSWER -
Local 94 answer - Place it in a container with ice water.
What is the main purpose for a crankcase breather line? - ANSWER -
The main purpose is to prevent oil from slugging the compressor.
pg. 4
FDNY Z51 EXAM 2 NEWEST 2025 ACTUAL EXAM|
COMPLETE 400 QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
ALREADY GRADED A+|FDNY Z51 WRITTEN
ACTUAL EXAM 2 |BRAND NEW!!
Which side of the compressor is R-22 vapor charged into? - ANSWER -
The suction side.
What should the percentage of lubricant circulated through a well-
designed system be? - ANSWER - Lubricant should not exceed 10%.
What is oil foaming in the compressor a result of? - ANSWER - Liquid
refrigerant in the crankcase.
What is the main reason for installing an oil separator on the discharge
line? - ANSWER - To return oil back to the compressor crank case.
What causes the foaming of oil in a reciprocating compressor using the
splash system for lubrication? - ANSWER - A rapid decrease in
pressure.
What is the purpose of oil in a refrigerant compressor? - ANSWER - It
reduces ware and friction.
pg. 1
,2|Page
What is a filter dryer used to remove? - ANSWER - Moisture, particles
and contaminants.
Where in a refrigeration system is the oil separator located? - ANSWER
- On the discharge line as far from the compressor as possible.
What accessory meters and controls the flow of refrigerant into the
evaporator? - ANSWER - The TEV (Metering Device).
What will occur if you use an automatic expansion valve with a variable
load? - ANSWER - You will starve the evaporator.
What does an automatic expansion valve do? - ANSWER - It maintains
a constant evaporator pressure.
What could cause the evaporator to not respond to the adjustments of the
TEV? - ANSWER - Oil logged on the low side.
What can non-condensable cause? - ANSWER - High head pressure.
When will compressor motor horsepower increase? - ANSWER - It will
increase as the head pressure increases.
When will compressor motor horsepower decrease? - ANSWER - As the
suction pressure increases.
pg. 2
,3|Page
When using a brine solution in a system what can be used to prevent
rusting? - ANSWER - Di-Chromate Tablets.
What would cause a Halide torch flame to turn yellow? - ANSWER - A
clogged sample tube.
What is the purpose of having 2 compressors in a cascade system? -
ANSWER - To operate and very low temperatures and avoid high
compression ratio.
Why is a pressure relief valve better than a fusible plug? - ANSWER -
Because it can be re-seated and is cost efficient.
What could cause compressor knocking? - ANSWER - Liquid
refrigerant slugging the compressor.
What would occur if a TEV'S spring were to break? - ANSWER - It
would flood the evaporator and raise the suction pressure because a TEV
uses spring pressure as its closing force. Thus, if the spring does not
close the TEV refrigerant will constantly be metered into the evaporator.
What is the purpose of the TEV equalizer line? - ANSWER - It
compensates for the pressure drop in the evaporator. Simply put, it
equalizes pressure drop lost across the evaporator.
pg. 3
, 4|Page
What should be done when installing copper pipe and a 90-degree elbow
is needed? - ANSWER - You should BRAZE in a FACTORY MADE
90-degree elbow.
What is the purpose of a service valve stem cap? - ANSWER - It
protects the valve from refrigerant leakage.
What advantage do semi hermetic compressors have over hermetic
compressor's? - ANSWER - Semi hermetic compressors can be serviced.
What happens when using portable compressor recovery unit to remove
vapor? - ANSWER - The vapor density is decreased.
What is the purpose of an unloader? - ANSWER - To decrease capacity
(capacity control).
What determines the amount of pressure that flows through the orifice
plates? - ANSWER - The difference in pressure between the high side
and the low side of the system.
How can you check proper operation of a thermometer? - ANSWER -
Local 94 answer - Place it in a container with ice water.
What is the main purpose for a crankcase breather line? - ANSWER -
The main purpose is to prevent oil from slugging the compressor.
pg. 4
