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(311) Washington DC Master Air Conditioning
(A/C) and Refrigeration Mechanical Unlimited
Exam | Latest Verified Questions and Detailed
Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the DC Master Air
Conditioning and Refrigeration Mechanical Unlimited (311) exam, an open-book
assessment that permits the use of approved references such as the 2012
International Mechanical Code and OSHA 1926 regulations. The exam evaluates a
candidate's knowledge across a broad range of advanced HVACR topics, including local
DC mechanical codes and safety protocols, refrigeration cycle theory and components,
system design and installation (piping, ductwork, chillers, cooling towers, and heat
pumps), electrical fundamentals and control schematics, troubleshooting and
maintenance practices, and environmental and energy-efficiency requirements. It is
administered by Prometric on behalf of the DC Department of Licensing and Consumer
Protection (DLCP) to qualify professionals for unlimited work on refrigeration and air
conditioning systems of any size or nature.
QUESTION 1
What is the minimum required clearance in front of a 480-volt electrical panel according
to OSHA 1926 Subpart K?
A) 24 inches
B) 30 inches
C) 36 inches
D) 42 inches
CORRECT ANSWER: C
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EXPERT RATIONALE: OSHA 1926.403 requires at least 3 feet of working clearance in
front of electrical equipment operating at 600 volts or less to ensure safe access and
operation.
QUESTION 2
Under the 2012 IMC, what is the minimum exhaust rate for a commercial restroom with
a water closet in CFM?
A) 25 CFM
B) 50 CFM
C) 70 CFM
D) 100 CFM
CORRECT ANSWER: B
EXPERT RATIONALE: Table 403.3 of the 2012 IMC specifies 50 CFM intermittent or 20
CFM continuous exhaust for each water closet in a public restroom.
QUESTION 3
Which refrigerant is classified as an A2L under ASHRAE Standard 34?
A) R-22
B) R-410A
C) R-32
D) R-134a
CORRECT ANSWER: C
EXPERT RATIONALE: R-32 has lower flammability (A2L), while R-22 and R-134a are A1
(nonflammable) and R-410A is A1. A2L refrigerants require specific safety measures.
QUESTION 4
In a vapor-compression refrigeration cycle, where is the refrigerant at its highest
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temperature?
A) Evaporator outlet
B) Compressor discharge
C) Condenser outlet
D) Metering device inlet
CORRECT ANSWER: B
EXPERT RATIONALE: The compressor discharge contains superheated vapor at the
highest temperature in the cycle due to the heat of compression added to the absorbed
heat from the evaporator.
QUESTION 5
What branch circuit conductor ampacity is required for a single 3-ton, 208V single-
phase air conditioner with a minimum circuit ampacity (MCA) of 20A and a maximum
overcurrent protection (MOP) of 35A?
A) 20A
B) 25A
C) 30A
D) 35A
CORRECT ANSWER: A
EXPERT RATIONALE: Conductors are sized based on MCA (20A), not MOP. The
overcurrent protective device can be up to 35A for starting, but the wire must carry the
MCA safely.
QUESTION 6
When recovering refrigerant from a low-pressure chiller, what is the maximum allowable
recovery vessel fill level?
A) 60% by weight
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B) 80% by weight
C) 80% by volume
D) 90% by volume
CORRECT ANSWER: C
EXPERT RATIONALE: Per EPA regulations, recovery cylinders must not be filled more
than 80% of their liquid volume to allow for thermal expansion, preventing hydrostatic
rupture.
QUESTION 7
In the District of Columbia, which code governs the installation of mechanical systems?
A) 2018 International Mechanical Code
B) 2012 DC Mechanical Code (based on 2012 IMC with amendments)
C) 2015 Uniform Mechanical Code
D) 2009 International Mechanical Code
CORRECT ANSWER: B
EXPERT RATIONALE: DC adopted the 2012 International Mechanical Code with local
amendments as the DC Mechanical Code. Always verify the current edition, but the
exam reference is the 2012 IMC.
QUESTION 8
What is the purpose of a crankcase heater on a compressor?
A) Prevent liquid slugging
B) Maintain oil temperature to reduce refrigerant migration
C) Increase compressor efficiency
D) Reduce discharge temperature
CORRECT ANSWER: B
(311) Washington DC Master Air Conditioning
(A/C) and Refrigeration Mechanical Unlimited
Exam | Latest Verified Questions and Detailed
Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the DC Master Air
Conditioning and Refrigeration Mechanical Unlimited (311) exam, an open-book
assessment that permits the use of approved references such as the 2012
International Mechanical Code and OSHA 1926 regulations. The exam evaluates a
candidate's knowledge across a broad range of advanced HVACR topics, including local
DC mechanical codes and safety protocols, refrigeration cycle theory and components,
system design and installation (piping, ductwork, chillers, cooling towers, and heat
pumps), electrical fundamentals and control schematics, troubleshooting and
maintenance practices, and environmental and energy-efficiency requirements. It is
administered by Prometric on behalf of the DC Department of Licensing and Consumer
Protection (DLCP) to qualify professionals for unlimited work on refrigeration and air
conditioning systems of any size or nature.
QUESTION 1
What is the minimum required clearance in front of a 480-volt electrical panel according
to OSHA 1926 Subpart K?
A) 24 inches
B) 30 inches
C) 36 inches
D) 42 inches
CORRECT ANSWER: C
,2|Page
EXPERT RATIONALE: OSHA 1926.403 requires at least 3 feet of working clearance in
front of electrical equipment operating at 600 volts or less to ensure safe access and
operation.
QUESTION 2
Under the 2012 IMC, what is the minimum exhaust rate for a commercial restroom with
a water closet in CFM?
A) 25 CFM
B) 50 CFM
C) 70 CFM
D) 100 CFM
CORRECT ANSWER: B
EXPERT RATIONALE: Table 403.3 of the 2012 IMC specifies 50 CFM intermittent or 20
CFM continuous exhaust for each water closet in a public restroom.
QUESTION 3
Which refrigerant is classified as an A2L under ASHRAE Standard 34?
A) R-22
B) R-410A
C) R-32
D) R-134a
CORRECT ANSWER: C
EXPERT RATIONALE: R-32 has lower flammability (A2L), while R-22 and R-134a are A1
(nonflammable) and R-410A is A1. A2L refrigerants require specific safety measures.
QUESTION 4
In a vapor-compression refrigeration cycle, where is the refrigerant at its highest
,3|Page
temperature?
A) Evaporator outlet
B) Compressor discharge
C) Condenser outlet
D) Metering device inlet
CORRECT ANSWER: B
EXPERT RATIONALE: The compressor discharge contains superheated vapor at the
highest temperature in the cycle due to the heat of compression added to the absorbed
heat from the evaporator.
QUESTION 5
What branch circuit conductor ampacity is required for a single 3-ton, 208V single-
phase air conditioner with a minimum circuit ampacity (MCA) of 20A and a maximum
overcurrent protection (MOP) of 35A?
A) 20A
B) 25A
C) 30A
D) 35A
CORRECT ANSWER: A
EXPERT RATIONALE: Conductors are sized based on MCA (20A), not MOP. The
overcurrent protective device can be up to 35A for starting, but the wire must carry the
MCA safely.
QUESTION 6
When recovering refrigerant from a low-pressure chiller, what is the maximum allowable
recovery vessel fill level?
A) 60% by weight
, 4|Page
B) 80% by weight
C) 80% by volume
D) 90% by volume
CORRECT ANSWER: C
EXPERT RATIONALE: Per EPA regulations, recovery cylinders must not be filled more
than 80% of their liquid volume to allow for thermal expansion, preventing hydrostatic
rupture.
QUESTION 7
In the District of Columbia, which code governs the installation of mechanical systems?
A) 2018 International Mechanical Code
B) 2012 DC Mechanical Code (based on 2012 IMC with amendments)
C) 2015 Uniform Mechanical Code
D) 2009 International Mechanical Code
CORRECT ANSWER: B
EXPERT RATIONALE: DC adopted the 2012 International Mechanical Code with local
amendments as the DC Mechanical Code. Always verify the current edition, but the
exam reference is the 2012 IMC.
QUESTION 8
What is the purpose of a crankcase heater on a compressor?
A) Prevent liquid slugging
B) Maintain oil temperature to reduce refrigerant migration
C) Increase compressor efficiency
D) Reduce discharge temperature
CORRECT ANSWER: B
