Chicago DOB – Mechanical Contractor License
Examination Questions and Correct Answers
(Verified Answers) Plus Rationale 2027 Q&A|
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1. What is the primary purpose of a mechanical ventilation system in
a building?
A. To increase structural loading capacity
B. To provide fresh air and remove contaminated or stale air
C. To eliminate the need for heating equipment
D. To reduce the size of electrical service
Answer: B. To provide fresh air and remove contaminated or stale air
Rationale: Mechanical ventilation is intended to introduce outdoor air
and remove stale, contaminated, humid, or otherwise undesirable air.
Proper ventilation supports acceptable indoor air quality and helps
control moisture and pollutants. It does not replace the structural or
electrical functions of the building.
, 2. Which component of an HVAC system is primarily responsible for
transferring heat from indoor air to a refrigerant during cooling?
A. Condenser
B. Evaporator
C. Compressor
D. Expansion valve
Answer: B. Evaporator
Rationale: In cooling operation, the evaporator absorbs heat from the
indoor air as refrigerant changes state and evaporates. The
compressor then raises the refrigerant pressure, while the condenser
rejects heat to the outdoor environment. The expansion device
reduces refrigerant pressure before the refrigerant enters the
evaporator.
3. What is the principal function of a refrigerant compressor?
A. Reduce refrigerant pressure
B. Remove moisture from supply air
C. Raise the pressure and temperature of refrigerant vapor
D. Convert liquid refrigerant directly into ice
Answer: C. Raise the pressure and temperature of refrigerant vapor
,Rationale: The compressor receives relatively low-pressure refrigerant
vapor from the evaporator and compresses it into a high-pressure,
higher-temperature vapor. This allows the refrigerant to reject heat
effectively in the condenser. Compression is therefore central to the
refrigeration cycle.
4. In a typical vapor-compression refrigeration system, where does
the refrigerant reject most of the heat it has absorbed?
A. Evaporator
B. Condenser
C. Expansion valve
D. Suction accumulator
Answer: B. Condenser
Rationale: The condenser receives hot, high-pressure refrigerant vapor
from the compressor. Heat is transferred from the refrigerant to the
surrounding air or water, causing the refrigerant to condense into a
liquid. The condenser therefore serves as the primary heat-rejection
component.
5. What is the purpose of an expansion valve or metering device in a
refrigeration system?
, A. Increase refrigerant pressure
B. Increase compressor speed
C. Reduce refrigerant pressure and regulate refrigerant flow
D. Remove oil from the compressor
Answer: C. Reduce refrigerant pressure and regulate refrigerant flow
Rationale: The metering device creates a pressure drop between the
high-pressure and low-pressure portions of the refrigeration system. It
also controls the quantity of refrigerant entering the evaporator.
Proper metering is essential for maintaining correct evaporator
operation and system performance.
6. Which condition is most likely to cause inadequate cooling from
an air-conditioning system?
A. Proper airflow and correct refrigerant charge
B. Severely restricted airflow across the evaporator
C. Correctly sized equipment
D. Clean filters and coils
Answer: B. Severely restricted airflow across the evaporator
Rationale: Restricted airflow reduces the amount of heat transferred
from the conditioned space to the evaporator. It can cause low
evaporator temperatures, reduced capacity, poor comfort, and
Examination Questions and Correct Answers
(Verified Answers) Plus Rationale 2027 Q&A|
Instant Download Pdf
1. What is the primary purpose of a mechanical ventilation system in
a building?
A. To increase structural loading capacity
B. To provide fresh air and remove contaminated or stale air
C. To eliminate the need for heating equipment
D. To reduce the size of electrical service
Answer: B. To provide fresh air and remove contaminated or stale air
Rationale: Mechanical ventilation is intended to introduce outdoor air
and remove stale, contaminated, humid, or otherwise undesirable air.
Proper ventilation supports acceptable indoor air quality and helps
control moisture and pollutants. It does not replace the structural or
electrical functions of the building.
, 2. Which component of an HVAC system is primarily responsible for
transferring heat from indoor air to a refrigerant during cooling?
A. Condenser
B. Evaporator
C. Compressor
D. Expansion valve
Answer: B. Evaporator
Rationale: In cooling operation, the evaporator absorbs heat from the
indoor air as refrigerant changes state and evaporates. The
compressor then raises the refrigerant pressure, while the condenser
rejects heat to the outdoor environment. The expansion device
reduces refrigerant pressure before the refrigerant enters the
evaporator.
3. What is the principal function of a refrigerant compressor?
A. Reduce refrigerant pressure
B. Remove moisture from supply air
C. Raise the pressure and temperature of refrigerant vapor
D. Convert liquid refrigerant directly into ice
Answer: C. Raise the pressure and temperature of refrigerant vapor
,Rationale: The compressor receives relatively low-pressure refrigerant
vapor from the evaporator and compresses it into a high-pressure,
higher-temperature vapor. This allows the refrigerant to reject heat
effectively in the condenser. Compression is therefore central to the
refrigeration cycle.
4. In a typical vapor-compression refrigeration system, where does
the refrigerant reject most of the heat it has absorbed?
A. Evaporator
B. Condenser
C. Expansion valve
D. Suction accumulator
Answer: B. Condenser
Rationale: The condenser receives hot, high-pressure refrigerant vapor
from the compressor. Heat is transferred from the refrigerant to the
surrounding air or water, causing the refrigerant to condense into a
liquid. The condenser therefore serves as the primary heat-rejection
component.
5. What is the purpose of an expansion valve or metering device in a
refrigeration system?
, A. Increase refrigerant pressure
B. Increase compressor speed
C. Reduce refrigerant pressure and regulate refrigerant flow
D. Remove oil from the compressor
Answer: C. Reduce refrigerant pressure and regulate refrigerant flow
Rationale: The metering device creates a pressure drop between the
high-pressure and low-pressure portions of the refrigeration system. It
also controls the quantity of refrigerant entering the evaporator.
Proper metering is essential for maintaining correct evaporator
operation and system performance.
6. Which condition is most likely to cause inadequate cooling from
an air-conditioning system?
A. Proper airflow and correct refrigerant charge
B. Severely restricted airflow across the evaporator
C. Correctly sized equipment
D. Clean filters and coils
Answer: B. Severely restricted airflow across the evaporator
Rationale: Restricted airflow reduces the amount of heat transferred
from the conditioned space to the evaporator. It can cause low
evaporator temperatures, reduced capacity, poor comfort, and
