Louisiana Mechanical Contractor
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
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1. What is the primary purpose of a mechanical contractor's
expansion tank in a closed hydronic heating system?
A. Increase pump horsepower
B. Store make-up water for domestic use
C. Absorb thermal expansion of the system fluid
D. Increase boiler firing rate
Answer: C. Absorb thermal expansion of the system fluid
Rationale: An expansion tank provides a compressible space that
accommodates the increase in water volume as system temperature
rises. Without adequate expansion accommodation, system pressure
can increase excessively and cause relief-valve discharge or equipment
damage.
2. Which refrigerant-side component removes heat from the
conditioned space in a conventional vapor-compression air-
conditioning system?
A. Condenser
B. Evaporator
C. Receiver
D. Compressor
,Answer: B. Evaporator
Rationale: The evaporator absorbs heat from the air or fluid being
cooled as refrigerant evaporates inside the coil. The compressor,
condenser, and expansion device perform different functions in
completing the refrigeration cycle.
3. What is the primary function of a compressor in a vapor-
compression refrigeration system?
A. Lower refrigerant pressure
B. Remove moisture from the air
C. Raise refrigerant vapor pressure and circulate refrigerant
D. Convert liquid refrigerant directly into ice
Answer: C. Raise refrigerant vapor pressure and circulate
refrigerant
Rationale: The compressor takes low-pressure refrigerant vapor from
the evaporator and compresses it into a high-pressure, high-
temperature vapor. This pressure increase permits the refrigerant to
reject heat in the condenser.
4. What is the purpose of a thermostatic expansion valve?
A. Increase condenser pressure
B. Meter refrigerant into the evaporator
C. Compress refrigerant vapor
D. Remove oil from the compressor
Answer: B. Meter refrigerant into the evaporator
Rationale: A thermostatic expansion valve regulates refrigerant flow
into the evaporator, generally responding to evaporator outlet
superheat. Proper metering helps maintain effective evaporator
operation and protects the compressor from liquid refrigerant return.
, 5. Superheat is best described as:
A. The temperature of liquid below its boiling point
B. The temperature of vapor above its saturation temperature
C. The temperature difference between condenser and ambient air
D. The pressure difference across a compressor
Answer: B. The temperature of vapor above its saturation
temperature
Rationale: Superheat is the amount by which a vapor's actual
temperature exceeds its saturation temperature at a given pressure.
Measuring superheat is important when evaluating evaporator
operation and refrigerant charge.
6. Subcooling refers to:
A. Cooling a vapor below its dew point
B. Cooling a liquid below its saturation temperature
C. Heating liquid refrigerant above its saturation temperature
D. Reducing compressor discharge pressure to zero
Answer: B. Cooling a liquid below its saturation temperature
Rationale: Subcooling is the temperature difference between the
saturation temperature and the actual temperature of a liquid
refrigerant. Adequate liquid subcooling can help ensure that solid
liquid refrigerant reaches the metering device.
7. Which component rejects heat from the refrigerant to the
surrounding medium?
A. Evaporator
B. Condenser
C. Expansion valve
D. Accumulator
, Answer: B. Condenser
Rationale: The condenser receives high-pressure, high-temperature
refrigerant vapor from the compressor and transfers heat to air or
water. As heat is rejected, the refrigerant changes from vapor to liquid.
8. What is the primary purpose of a liquid-line filter-drier?
A. Increase compressor speed
B. Remove contaminants and moisture from the refrigerant circuit
C. Increase evaporator temperature
D. Add refrigerant oil
Answer: B. Remove contaminants and moisture from the refrigerant
circuit
Rationale: A filter-drier traps particulate contaminants and absorbs
moisture that could otherwise damage components or cause chemical
and operational problems. It is normally installed in the liquid line in
many systems.
9. What condition can occur when excessive liquid refrigerant enters
a compressor?
A. Refrigerant migration only
B. Liquid slugging
C. Improved lubrication
D. Increased compressor efficiency
Answer: B. Liquid slugging
Rationale: Compressors are designed primarily to compress vapor.
Liquid entering the compression chamber can cause mechanical
damage because liquid is essentially incompressible.
Examination Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a mechanical contractor's
expansion tank in a closed hydronic heating system?
A. Increase pump horsepower
B. Store make-up water for domestic use
C. Absorb thermal expansion of the system fluid
D. Increase boiler firing rate
Answer: C. Absorb thermal expansion of the system fluid
Rationale: An expansion tank provides a compressible space that
accommodates the increase in water volume as system temperature
rises. Without adequate expansion accommodation, system pressure
can increase excessively and cause relief-valve discharge or equipment
damage.
2. Which refrigerant-side component removes heat from the
conditioned space in a conventional vapor-compression air-
conditioning system?
A. Condenser
B. Evaporator
C. Receiver
D. Compressor
,Answer: B. Evaporator
Rationale: The evaporator absorbs heat from the air or fluid being
cooled as refrigerant evaporates inside the coil. The compressor,
condenser, and expansion device perform different functions in
completing the refrigeration cycle.
3. What is the primary function of a compressor in a vapor-
compression refrigeration system?
A. Lower refrigerant pressure
B. Remove moisture from the air
C. Raise refrigerant vapor pressure and circulate refrigerant
D. Convert liquid refrigerant directly into ice
Answer: C. Raise refrigerant vapor pressure and circulate
refrigerant
Rationale: The compressor takes low-pressure refrigerant vapor from
the evaporator and compresses it into a high-pressure, high-
temperature vapor. This pressure increase permits the refrigerant to
reject heat in the condenser.
4. What is the purpose of a thermostatic expansion valve?
A. Increase condenser pressure
B. Meter refrigerant into the evaporator
C. Compress refrigerant vapor
D. Remove oil from the compressor
Answer: B. Meter refrigerant into the evaporator
Rationale: A thermostatic expansion valve regulates refrigerant flow
into the evaporator, generally responding to evaporator outlet
superheat. Proper metering helps maintain effective evaporator
operation and protects the compressor from liquid refrigerant return.
, 5. Superheat is best described as:
A. The temperature of liquid below its boiling point
B. The temperature of vapor above its saturation temperature
C. The temperature difference between condenser and ambient air
D. The pressure difference across a compressor
Answer: B. The temperature of vapor above its saturation
temperature
Rationale: Superheat is the amount by which a vapor's actual
temperature exceeds its saturation temperature at a given pressure.
Measuring superheat is important when evaluating evaporator
operation and refrigerant charge.
6. Subcooling refers to:
A. Cooling a vapor below its dew point
B. Cooling a liquid below its saturation temperature
C. Heating liquid refrigerant above its saturation temperature
D. Reducing compressor discharge pressure to zero
Answer: B. Cooling a liquid below its saturation temperature
Rationale: Subcooling is the temperature difference between the
saturation temperature and the actual temperature of a liquid
refrigerant. Adequate liquid subcooling can help ensure that solid
liquid refrigerant reaches the metering device.
7. Which component rejects heat from the refrigerant to the
surrounding medium?
A. Evaporator
B. Condenser
C. Expansion valve
D. Accumulator
, Answer: B. Condenser
Rationale: The condenser receives high-pressure, high-temperature
refrigerant vapor from the compressor and transfers heat to air or
water. As heat is rejected, the refrigerant changes from vapor to liquid.
8. What is the primary purpose of a liquid-line filter-drier?
A. Increase compressor speed
B. Remove contaminants and moisture from the refrigerant circuit
C. Increase evaporator temperature
D. Add refrigerant oil
Answer: B. Remove contaminants and moisture from the refrigerant
circuit
Rationale: A filter-drier traps particulate contaminants and absorbs
moisture that could otherwise damage components or cause chemical
and operational problems. It is normally installed in the liquid line in
many systems.
9. What condition can occur when excessive liquid refrigerant enters
a compressor?
A. Refrigerant migration only
B. Liquid slugging
C. Improved lubrication
D. Increased compressor efficiency
Answer: B. Liquid slugging
Rationale: Compressors are designed primarily to compress vapor.
Liquid entering the compression chamber can cause mechanical
damage because liquid is essentially incompressible.
