FDNY Z51 WRITTEN EXAM ACTUAL EXAM 2 VERSIONS (VERSION A AND B) COMPLETE EXAM QUESTIONS WITH DETAILED VERIFIED ANSWERS / ALREADY GRADED A+

FDNY Z51 WRITTEN EXAM ACTUAL EXAM 2 VERSIONS
(VERSION A AND B) COMPLETE EXAM QUESTIONS WITH
DETAILED VERIFIED ANSWERS / ALREADY GRADED A+

Question 1
The efficiency of a refrigerant cycle is significantly affected by the operation
of the condenser. Which of the following conditions would result in a more
efficient centrifugal compressor operation?
A) Increasing the condensing pressure.
B) Raising the evaporator temperature.
C) Maintaining a higher discharge temperature.
D) Lowering the condensing pressure.
E) Increasing the compressor's rotational speed.
Correct Answer: D) Lowering the condensing pressure
Rationale: Lowering the condensing pressure reduces the
compression ratio and the work required by the centrifugal
compressor, thereby improving its overall efficiency.

Question 2
The heat removed from the refrigerant in a condenser during the
refrigeration cycle is primarily what type of heat?
A) Only sensible heat.
B) Only latent heat.
C) Sensible and latent heat.
D) Superheat only.
E) Subcooling only.
Correct Answer: C) Sensible and latent heat
Rationale: The condenser first removes superheat (sensible heat)
from the refrigerant vapor, then removes latent heat as the
refrigerant condenses from vapor to liquid, and finally removes
sensible heat as the liquid subcools.

Question 3
The refrigerant unit you have been assigned to is being taken out of service
for a major repair. You must withdraw refrigerant for storage in suitable

,containers. According to the New York City Fire Code, you must ensure that
these containers:
A) Are made of any non-corrosive metal.
B) Are approved by the US Department of Transportation.
C) Are clearly labeled with the date of withdrawal only.
D) Can be filled to 100% capacity.
E) Are stored in direct sunlight for inspection.
Correct Answer: B) Are approved by the US Department of
Transportation
Rationale: Refrigerant storage containers (recovery cylinders) must
meet DOT specifications to ensure their safe handling, transport,
and storage, as refrigerants are pressurized substances.

Question 4
Which of the following best describes how a cylinder unloader works in a
reciprocating compressor?
A) It opens the discharge valve during the compression stroke.
B) It closes the suction valve during the compression stroke.
C) It keeps the suction valve open while the compressor is in the return
stroke.
D) It bypasses refrigerant from the discharge directly to the suction side.
E) It reduces the compressor's motor speed.
Correct Answer: C) Keeps in the suction valve opened while the
compressor is in the return stroke
Rationale: By holding the suction valve open during the return stroke,
the refrigerant is simply pushed back into the suction line instead of
being compressed, effectively reducing the capacity of that cylinder.

Question 5
In most semi-hermetic compressors, what is the suction vapor commonly
used for?
A) To lubricate the moving parts.

,B) To cool the motor.
C) To increase the discharge pressure.
D) To preheat the refrigerant before compression.
E) To assist in oil separation.
Correct Answer: B) Cool the motor
Rationale: In semi-hermetic compressors, the cool suction vapor is
often routed over the motor windings before entering the
compression chambers to dissipate heat generated by the motor,
thus protecting it from overheating.

Question 6
The amount of refrigerant that flows through the orifices of an economizer is
primarily determined by:
A) The compressor's discharge temperature.
B) The difference between the high side and low side pressure.
C) The refrigerant's specific heat capacity.
D) The evaporator's superheat.
E) The cooling tower's water temperature.
Correct Answer: B) Difference between the high side and load side
pressure
Rationale: Economizers often use a pressure differential to flash
liquid refrigerant into vapor, with the amount flowing determined by
the pressure difference between the high-pressure liquid line and a
lower-pressure point in the system (e.g., intermediate stage of
compression).

Question 7
The installation of an in-line refrigerant cleaning system is advisable under
which circumstance?
A) To simply increase refrigerant volume.
B) To remove impurities from the system.
C) To boost compressor efficiency instantly.

, D) To replace the need for regular oil changes.
E) To adjust system pressures.
Correct Answer: B) To remove impurities from the system
Rationale: In-line cleaning systems (e.g., filter-driers, reclaimers) are
used to continuously remove contaminants like moisture, acids, and
solid particles that can degrade refrigerant, lubricate oil, and
damage system components.

Question 8
Which type of refrigerant system is least likely to leak refrigerant directly into
the building spaces that are cooled?
A) Direct expansion system.
B) Variable refrigerant flow (VRF) system.
C) The indirect system.
D) Split system.
E) Packaged terminal air conditioner (PTAC).
Correct Answer: C) The indirect system
Rationale: In an indirect system, a secondary refrigerant (e.g., chilled
water or brine) circulates through the building spaces, while the
primary refrigerant remains contained within the chiller itself,
minimizing the risk of a direct refrigerant leak into occupied areas.

Question 9
The suction pressure of a reciprocating compressor is 65 PSIG. The discharge
pressure of this compressor is 120 PSIG. The atmospheric pressure is 14.7
PSI. The compression ratio for the given condition is closest to:
A) 1.25
B) 1.69
C) 1.95
D) 2.30
E) 1.50
Correct Answer: B) 1.69