DC Master Air Conditioning and Refrigeration
Mechanical Unlimited Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the primary purpose of a superheat measurement in a
refrigeration system?
A. To determine the subcooling of the refrigerant
B. To ensure the evaporator is fully flooded
C. To prevent liquid refrigerant from entering the compressor
D. To measure the condenser pressure
Rationale: Superheat is the temperature of the refrigerant vapor above
its saturation temperature. Proper superheat ensures that only vapor
enters the compressor, preventing potential mechanical damage from
liquid refrigerant.
2. Which of the following refrigerants has zero ozone depletion
potential?
A. R-12
, B. R-22
C. R-410A
D. R-502
Rationale: R-410A is a hydrofluorocarbon (HFC) with no chlorine
content, meaning it does not deplete the ozone layer, unlike CFCs (R-12)
and HCFCs (R-22).
3. The primary function of an expansion device is to:
A. Compress refrigerant
B. Condense refrigerant
C. Regulate refrigerant flow into the evaporator
D. Filter refrigerant
Rationale: Expansion devices (capillary tubes or thermostatic expansion
valves) reduce refrigerant pressure and meter it into the evaporator at
the correct rate for heat absorption.
4. In a direct expansion cooling system, what indicates a flooded
evaporator?
A. High superheat
B. Low or zero superheat
C. High subcooling
D. Low condensing pressure
,Rationale: A flooded evaporator occurs when refrigerant vapor is
minimal or absent leaving the evaporator. Superheat will be low or zero
because the vapor hasn’t absorbed enough heat to fully vaporize.
5. Which type of compressor is commonly used in large commercial
air conditioning systems?
A. Reciprocating
B. Screw
C. Centrifugal pump
D. Scroll
Rationale: Screw compressors are efficient for large systems with high-
capacity needs, providing continuous compression with fewer pulsations
compared to reciprocating types.
6. What is the function of a liquid line sight glass in a refrigeration
system?
A. Measure superheat
B. Observe refrigerant flow and detect moisture
C. Control compressor speed
D. Regulate condenser pressure
Rationale: Sight glasses allow technicians to visually confirm refrigerant
presence and detect bubbles indicating low charge or moisture, helping
prevent system issues.
, 7. Which component removes heat from the refrigerant in a
refrigeration cycle?
A. Evaporator
B. Expansion valve
C. Condenser
D. Compressor
Rationale: The condenser transfers heat from the high-pressure
refrigerant vapor to the outside environment, condensing it into a liquid.
8. What is the purpose of subcooling in a refrigeration system?
A. Prevent compressor overheating
B. Increase evaporator efficiency
C. Ensure refrigerant enters the expansion device as a liquid
D. Increase condenser pressure
Rationale: Subcooling lowers refrigerant temperature below saturation,
ensuring liquid state entering the expansion device, preventing flash gas
and maintaining efficiency.
9. In an HVACR system, what is the effect of overcharging the
refrigerant?
A. Increased superheat
B. Higher pressures and possible compressor damage
Mechanical Unlimited Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download Pdf
1. What is the primary purpose of a superheat measurement in a
refrigeration system?
A. To determine the subcooling of the refrigerant
B. To ensure the evaporator is fully flooded
C. To prevent liquid refrigerant from entering the compressor
D. To measure the condenser pressure
Rationale: Superheat is the temperature of the refrigerant vapor above
its saturation temperature. Proper superheat ensures that only vapor
enters the compressor, preventing potential mechanical damage from
liquid refrigerant.
2. Which of the following refrigerants has zero ozone depletion
potential?
A. R-12
, B. R-22
C. R-410A
D. R-502
Rationale: R-410A is a hydrofluorocarbon (HFC) with no chlorine
content, meaning it does not deplete the ozone layer, unlike CFCs (R-12)
and HCFCs (R-22).
3. The primary function of an expansion device is to:
A. Compress refrigerant
B. Condense refrigerant
C. Regulate refrigerant flow into the evaporator
D. Filter refrigerant
Rationale: Expansion devices (capillary tubes or thermostatic expansion
valves) reduce refrigerant pressure and meter it into the evaporator at
the correct rate for heat absorption.
4. In a direct expansion cooling system, what indicates a flooded
evaporator?
A. High superheat
B. Low or zero superheat
C. High subcooling
D. Low condensing pressure
,Rationale: A flooded evaporator occurs when refrigerant vapor is
minimal or absent leaving the evaporator. Superheat will be low or zero
because the vapor hasn’t absorbed enough heat to fully vaporize.
5. Which type of compressor is commonly used in large commercial
air conditioning systems?
A. Reciprocating
B. Screw
C. Centrifugal pump
D. Scroll
Rationale: Screw compressors are efficient for large systems with high-
capacity needs, providing continuous compression with fewer pulsations
compared to reciprocating types.
6. What is the function of a liquid line sight glass in a refrigeration
system?
A. Measure superheat
B. Observe refrigerant flow and detect moisture
C. Control compressor speed
D. Regulate condenser pressure
Rationale: Sight glasses allow technicians to visually confirm refrigerant
presence and detect bubbles indicating low charge or moisture, helping
prevent system issues.
, 7. Which component removes heat from the refrigerant in a
refrigeration cycle?
A. Evaporator
B. Expansion valve
C. Condenser
D. Compressor
Rationale: The condenser transfers heat from the high-pressure
refrigerant vapor to the outside environment, condensing it into a liquid.
8. What is the purpose of subcooling in a refrigeration system?
A. Prevent compressor overheating
B. Increase evaporator efficiency
C. Ensure refrigerant enters the expansion device as a liquid
D. Increase condenser pressure
Rationale: Subcooling lowers refrigerant temperature below saturation,
ensuring liquid state entering the expansion device, preventing flash gas
and maintaining efficiency.
9. In an HVACR system, what is the effect of overcharging the
refrigerant?
A. Increased superheat
B. Higher pressures and possible compressor damage
