FDNY Z-51 Written Exam 2026/2027 – Practice Test Bank & Study
Guide
Refrigerating System Operating Engineer (RSOE) Certification
Section 1: Refrigeration Fundamentals & Cycle (Questions 1–
25)
1. What are the four main components of the vapor-
compression refrigeration cycle?
A) Compressor, condenser, expansion valve, evaporator
B) Compressor, receiver, accumulator, evaporator
C) Condenser, cooling tower, pump, chiller
D) Evaporator, absorber, generator, condenser
Answer A: — Compressor, condenser, expansion valve,
evaporator
,Rationale: The vapor-compression refrigeration cycle consists of
four main components: the compressor (raises pressure and
temperature of refrigerant vapor), the condenser (rejects heat and
condenses refrigerant to liquid), the expansion valve (reduces
pressure and controls refrigerant flow), and the evaporator
(absorbs heat and evaporates refrigerant). ---
2. The most important reason to sub-cool the refrigerant in
the condenser is to ensure that:
A) A pure liquid refrigerant will enter the metering device
B) The compressor discharge temperature is reduced
C) The evaporator pressure is increased
D) The condenser pressure is reduced
Answer A: — A pure liquid refrigerant will enter the metering
device
Rationale: Sub-cooling ensures that refrigerant entering the
metering device (expansion valve) is 100% liquid, preventing
flash gas from forming before the expansion valve. This maximizes
the refrigeration effect and system efficiency. ---
,3. What is the primary function of a refrigeration system?
A) Generate electricity
B) Remove heat from a designated space or substance
C) Produce heat for a building
D) Filter air particles
Answer B: — Remove heat from a designated space or
substance
Rationale: The primary function of a refrigeration system is to
remove heat from a designated space or substance, transferring it
to another location where it can be rejected. ---
4. When an expansion valve is operating properly, at the end
of the evaporator will contain:
A) Only superheated vapor
B) Only liquid refrigerant
C) A mixture of liquid and vapor
D) Subcooled liquid
Answer A: — Only superheated vapor
Rationale: A properly operating expansion valve maintains the
correct refrigerant flow so that all liquid refrigerant is fully
, evaporated by the end of the evaporator, resulting in only
superheated vapor entering the compressor suction line. ---
5. In order for a refrigerant to become superheated, it must
be heated in a section of the low side refrigerant line:
A) Where no liquid refrigerant is present
B) Where liquid refrigerant is present
C) In the condenser
D) In the receiver
Answer A: — Where no liquid refrigerant is present
Rationale: Superheating occurs when refrigerant vapor is heated
above its saturation temperature in a section of the low-side line
where no liquid refrigerant remains. This ensures all liquid has
evaporated before entering the compressor. ---
6. The heat removed from the refrigerant in a condenser is:
A) Sensible and latent heat
B) Only sensible heat
C) Only latent heat
D) Neither sensible nor latent heat
Guide
Refrigerating System Operating Engineer (RSOE) Certification
Section 1: Refrigeration Fundamentals & Cycle (Questions 1–
25)
1. What are the four main components of the vapor-
compression refrigeration cycle?
A) Compressor, condenser, expansion valve, evaporator
B) Compressor, receiver, accumulator, evaporator
C) Condenser, cooling tower, pump, chiller
D) Evaporator, absorber, generator, condenser
Answer A: — Compressor, condenser, expansion valve,
evaporator
,Rationale: The vapor-compression refrigeration cycle consists of
four main components: the compressor (raises pressure and
temperature of refrigerant vapor), the condenser (rejects heat and
condenses refrigerant to liquid), the expansion valve (reduces
pressure and controls refrigerant flow), and the evaporator
(absorbs heat and evaporates refrigerant). ---
2. The most important reason to sub-cool the refrigerant in
the condenser is to ensure that:
A) A pure liquid refrigerant will enter the metering device
B) The compressor discharge temperature is reduced
C) The evaporator pressure is increased
D) The condenser pressure is reduced
Answer A: — A pure liquid refrigerant will enter the metering
device
Rationale: Sub-cooling ensures that refrigerant entering the
metering device (expansion valve) is 100% liquid, preventing
flash gas from forming before the expansion valve. This maximizes
the refrigeration effect and system efficiency. ---
,3. What is the primary function of a refrigeration system?
A) Generate electricity
B) Remove heat from a designated space or substance
C) Produce heat for a building
D) Filter air particles
Answer B: — Remove heat from a designated space or
substance
Rationale: The primary function of a refrigeration system is to
remove heat from a designated space or substance, transferring it
to another location where it can be rejected. ---
4. When an expansion valve is operating properly, at the end
of the evaporator will contain:
A) Only superheated vapor
B) Only liquid refrigerant
C) A mixture of liquid and vapor
D) Subcooled liquid
Answer A: — Only superheated vapor
Rationale: A properly operating expansion valve maintains the
correct refrigerant flow so that all liquid refrigerant is fully
, evaporated by the end of the evaporator, resulting in only
superheated vapor entering the compressor suction line. ---
5. In order for a refrigerant to become superheated, it must
be heated in a section of the low side refrigerant line:
A) Where no liquid refrigerant is present
B) Where liquid refrigerant is present
C) In the condenser
D) In the receiver
Answer A: — Where no liquid refrigerant is present
Rationale: Superheating occurs when refrigerant vapor is heated
above its saturation temperature in a section of the low-side line
where no liquid refrigerant remains. This ensures all liquid has
evaporated before entering the compressor. ---
6. The heat removed from the refrigerant in a condenser is:
A) Sensible and latent heat
B) Only sensible heat
C) Only latent heat
D) Neither sensible nor latent heat
