Nevada C-21B Air Conditioning Contractor Practice Exam Practice
Questions & Detailed Answers | Latest Update | A+ Graded
Question 1: According to standard refrigeration theory, what is the primary function of a thermostatic
expansion valve (TXV) in a vapor-compression refrigeration system?
A. To regulate the flow of high-pressure liquid refrigerant into the evaporator based on evaporator
superheat
B. To compress low-pressure refrigerant vapor into high-pressure superheated vapor
C. To reject heat from the high-pressure refrigerant gas to the outside ambient air
D. To collect liquid refrigerant and prevent it from flooding back into the compressor
CORRECT ANSWER: A. To regulate the flow of high-pressure liquid refrigerant into the evaporator
based on evaporator superheat
Rationale: The thermostatic expansion valve (TXV) meters the correct amount of liquid refrigerant
entering the evaporator coil by maintaining a constant superheat at the evaporator outlet, ensuring
maximum efficiency and compressor protection.
Question 2: Under the Nevada Contractors Board regulations, what is the maximum monetary fine or
disciplinary action typically associated with operating as a specialty contractor outside the scope of your
specific classification without a proper license modification?
A. A verbal warning and mandatory 30-day compliance period
B. Administrative fines, suspension, or revocation of the contractor's license along with potential criminal
misdemeanor charges
C. A fixed administrative fee of exactly $100 payable within 10 business days
D. Mandatory transfer to a residential general building classification
CORRECT ANSWER: B. Administrative fines, suspension, or revocation of the contractor's license along
with potential criminal misdemeanor charges
Rationale: The Nevada State Contractors Board (NSCB) enforces strict licensing boundaries. Contracting
outside of one's classification (such as performing electrical or plumbing work not covered under specific
specialty limits without proper dual-licensing) carries severe administrative penalties, license revocation,
and misdemeanor prosecution.
,Question 3: When sizing residential ductwork using the Air Conditioning Contractors of America (ACCA)
Manual D methodology, what is the standard maximum recommended friction rate loss per 100 feet of
equivalent duct length for typical residential systems?
A. 0.01 inches of water column
B. 0.05 to 0.10 inches of water column
C. 0.50 to 1.00 inches of water column
D. 2.00 inches of water column
CORRECT ANSWER: B. 0.05 to 0.10 inches of water column
Rationale: ACCA Manual D standard design practices typically utilize a friction rate between 0.05 and
0.10 inches of water column (wc) per 100 equivalent feet to balance static pressure drops across supply
and return duct runs efficiently.
Question 4: In an indirect-fired gas furnace, what safety device is designed to prove that the draft inducer
fan is operating properly before the gas valve is allowed to open?
A. Flame rollout switch
B. Pressure switch
C. High-limit control thermostat
D. Bi-metal fan and limit switch
CORRECT ANSWER: B. Pressure switch
Rationale: The draft proving pressure switch verifies that the induced draft blower is creating sufficient
negative pressure (or positive pressure in condensing units) to safely evacuate combustion gases before
the main gas valve energizes.
Question 5: Which of the following refrigerants is classified as an HFO (hydrofluoroolefin) with an ultra-
low Global Warming Potential (GWP) and is commonly used as a low-GWP alternative in modern HVAC
systems?
A. R-22
B. R-410A
C. R-1234yf
D. R-717
CORRECT ANSWER: C. R-1234yf
,Rationale: R-1234yf is a hydrofluoroolefin (HFO) refrigerant with a GWP of less than 1, making it an
environmentally friendly replacement designed to meet stringent EPA and international phase-down
regulations.
Question 6: According to OSHA safety standards regarding excavations and trenching on construction
sites, at what trench depth is a protective system (such as shoring, sloping, or trench shielding)
mandatory unless the excavation is entirely in stable rock?
A. 3 feet or deeper
B. 5 feet or deeper
C. 8 feet or deeper
D. 12 feet or deeper
CORRECT ANSWER: B. 5 feet or deeper
Rationale: OSHA regulations (29 CFR 1926.652) require that all employees in excavations 5 feet (1.5
meters) or deeper be protected by an approved excavation protective system unless the excavation is
made entirely in stable rock.
Question 7: What is the primary purpose of subcooling liquid refrigerant in a condenser coil?
A. To ensure that 100 percent liquid enters the expansion device without flashing into vapor prematurely
in the liquid line
B. To raise the temperature of the refrigerant above its critical saturation point
C. To decrease the compressor discharge pressure and reduce overall power consumption
D. To boil off residual lubricating oil trapped in the liquid line filter-drier
CORRECT ANSWER: A. To ensure that 100 percent liquid enters the expansion device without flashing
into vapor prematurely in the liquid line
Rationale: Subcooling cools the liquid refrigerant below its saturation temperature at a given pressure,
providing a safety margin against pressure drops in the liquid line that could otherwise cause flashing
before the refrigerant reaches the expansion valve.
Question 8: In electrical troubleshooting for HVAC equipment, what instrument and measurement setting
should a technician use to verify that a contactor coil is receiving the correct control voltage while the
unit is energized?
A. An ohmmeter set to measure resistance in ohms
B. A voltmeter set to measure alternating current (AC) voltage across the coil terminals
, C. An ammeter set to measure continuous microamps
D. A megohmmeter set to 500 volts DC
CORRECT ANSWER: B. A voltmeter set to measure alternating current (AC) voltage across the coil
terminals
Rationale: To check if a control circuit component like a contactor coil is energized, a digital multimeter
set to AC volts must be placed in parallel across the two coil terminals while the thermostat calls for
operation.
Question 9: When calculating total cooling load for a residential structure in southern Nevada (such as
Las Vegas) using ACCA Manual J, which factor has the most significant impact on peak sensible heat gain
during summer months?
A. Interior lighting loads from LED bulbs
B. Solar heat gain through windows and glass doors
C. Latent moisture gain from indoor houseplants
D. Heat generated by standard kitchen refrigerators
CORRECT ANSWER: B. Solar heat gain through windows and glass doors
Rationale: In desert climates like southern Nevada, direct solar radiation entering through windows
(fenestration) represents one of the largest components of the peak sensible cooling load in residential
Manual J calculations.
Question 10: Which of the following describes the correct procedure for recovering refrigerant from a
system prior to servicing, in compliance with EPA Section 608 regulations?
A. Venting the refrigerant directly to the outdoor atmosphere if it is an HFC
B. Using an EPA-certified recovery machine to pull the system down to the required vacuum level and
storing the refrigerant in an approved recovery cylinder
C. Flushing the refrigerant out using compressed nitrogen gas
D. Boiling off the refrigerant through open service ports using a torch
CORRECT ANSWER: B. Using an EPA-certified recovery machine to pull the system down to the
required vacuum level and storing the refrigerant in an approved recovery cylinder
Rationale: EPA Section 608 regulations strictly prohibit the intentional venting of regulated refrigerants
and mandate the use of certified recovery equipment and DOT-approved recovery tanks.
Questions & Detailed Answers | Latest Update | A+ Graded
Question 1: According to standard refrigeration theory, what is the primary function of a thermostatic
expansion valve (TXV) in a vapor-compression refrigeration system?
A. To regulate the flow of high-pressure liquid refrigerant into the evaporator based on evaporator
superheat
B. To compress low-pressure refrigerant vapor into high-pressure superheated vapor
C. To reject heat from the high-pressure refrigerant gas to the outside ambient air
D. To collect liquid refrigerant and prevent it from flooding back into the compressor
CORRECT ANSWER: A. To regulate the flow of high-pressure liquid refrigerant into the evaporator
based on evaporator superheat
Rationale: The thermostatic expansion valve (TXV) meters the correct amount of liquid refrigerant
entering the evaporator coil by maintaining a constant superheat at the evaporator outlet, ensuring
maximum efficiency and compressor protection.
Question 2: Under the Nevada Contractors Board regulations, what is the maximum monetary fine or
disciplinary action typically associated with operating as a specialty contractor outside the scope of your
specific classification without a proper license modification?
A. A verbal warning and mandatory 30-day compliance period
B. Administrative fines, suspension, or revocation of the contractor's license along with potential criminal
misdemeanor charges
C. A fixed administrative fee of exactly $100 payable within 10 business days
D. Mandatory transfer to a residential general building classification
CORRECT ANSWER: B. Administrative fines, suspension, or revocation of the contractor's license along
with potential criminal misdemeanor charges
Rationale: The Nevada State Contractors Board (NSCB) enforces strict licensing boundaries. Contracting
outside of one's classification (such as performing electrical or plumbing work not covered under specific
specialty limits without proper dual-licensing) carries severe administrative penalties, license revocation,
and misdemeanor prosecution.
,Question 3: When sizing residential ductwork using the Air Conditioning Contractors of America (ACCA)
Manual D methodology, what is the standard maximum recommended friction rate loss per 100 feet of
equivalent duct length for typical residential systems?
A. 0.01 inches of water column
B. 0.05 to 0.10 inches of water column
C. 0.50 to 1.00 inches of water column
D. 2.00 inches of water column
CORRECT ANSWER: B. 0.05 to 0.10 inches of water column
Rationale: ACCA Manual D standard design practices typically utilize a friction rate between 0.05 and
0.10 inches of water column (wc) per 100 equivalent feet to balance static pressure drops across supply
and return duct runs efficiently.
Question 4: In an indirect-fired gas furnace, what safety device is designed to prove that the draft inducer
fan is operating properly before the gas valve is allowed to open?
A. Flame rollout switch
B. Pressure switch
C. High-limit control thermostat
D. Bi-metal fan and limit switch
CORRECT ANSWER: B. Pressure switch
Rationale: The draft proving pressure switch verifies that the induced draft blower is creating sufficient
negative pressure (or positive pressure in condensing units) to safely evacuate combustion gases before
the main gas valve energizes.
Question 5: Which of the following refrigerants is classified as an HFO (hydrofluoroolefin) with an ultra-
low Global Warming Potential (GWP) and is commonly used as a low-GWP alternative in modern HVAC
systems?
A. R-22
B. R-410A
C. R-1234yf
D. R-717
CORRECT ANSWER: C. R-1234yf
,Rationale: R-1234yf is a hydrofluoroolefin (HFO) refrigerant with a GWP of less than 1, making it an
environmentally friendly replacement designed to meet stringent EPA and international phase-down
regulations.
Question 6: According to OSHA safety standards regarding excavations and trenching on construction
sites, at what trench depth is a protective system (such as shoring, sloping, or trench shielding)
mandatory unless the excavation is entirely in stable rock?
A. 3 feet or deeper
B. 5 feet or deeper
C. 8 feet or deeper
D. 12 feet or deeper
CORRECT ANSWER: B. 5 feet or deeper
Rationale: OSHA regulations (29 CFR 1926.652) require that all employees in excavations 5 feet (1.5
meters) or deeper be protected by an approved excavation protective system unless the excavation is
made entirely in stable rock.
Question 7: What is the primary purpose of subcooling liquid refrigerant in a condenser coil?
A. To ensure that 100 percent liquid enters the expansion device without flashing into vapor prematurely
in the liquid line
B. To raise the temperature of the refrigerant above its critical saturation point
C. To decrease the compressor discharge pressure and reduce overall power consumption
D. To boil off residual lubricating oil trapped in the liquid line filter-drier
CORRECT ANSWER: A. To ensure that 100 percent liquid enters the expansion device without flashing
into vapor prematurely in the liquid line
Rationale: Subcooling cools the liquid refrigerant below its saturation temperature at a given pressure,
providing a safety margin against pressure drops in the liquid line that could otherwise cause flashing
before the refrigerant reaches the expansion valve.
Question 8: In electrical troubleshooting for HVAC equipment, what instrument and measurement setting
should a technician use to verify that a contactor coil is receiving the correct control voltage while the
unit is energized?
A. An ohmmeter set to measure resistance in ohms
B. A voltmeter set to measure alternating current (AC) voltage across the coil terminals
, C. An ammeter set to measure continuous microamps
D. A megohmmeter set to 500 volts DC
CORRECT ANSWER: B. A voltmeter set to measure alternating current (AC) voltage across the coil
terminals
Rationale: To check if a control circuit component like a contactor coil is energized, a digital multimeter
set to AC volts must be placed in parallel across the two coil terminals while the thermostat calls for
operation.
Question 9: When calculating total cooling load for a residential structure in southern Nevada (such as
Las Vegas) using ACCA Manual J, which factor has the most significant impact on peak sensible heat gain
during summer months?
A. Interior lighting loads from LED bulbs
B. Solar heat gain through windows and glass doors
C. Latent moisture gain from indoor houseplants
D. Heat generated by standard kitchen refrigerators
CORRECT ANSWER: B. Solar heat gain through windows and glass doors
Rationale: In desert climates like southern Nevada, direct solar radiation entering through windows
(fenestration) represents one of the largest components of the peak sensible cooling load in residential
Manual J calculations.
Question 10: Which of the following describes the correct procedure for recovering refrigerant from a
system prior to servicing, in compliance with EPA Section 608 regulations?
A. Venting the refrigerant directly to the outdoor atmosphere if it is an HFC
B. Using an EPA-certified recovery machine to pull the system down to the required vacuum level and
storing the refrigerant in an approved recovery cylinder
C. Flushing the refrigerant out using compressed nitrogen gas
D. Boiling off the refrigerant through open service ports using a torch
CORRECT ANSWER: B. Using an EPA-certified recovery machine to pull the system down to the
required vacuum level and storing the refrigerant in an approved recovery cylinder
Rationale: EPA Section 608 regulations strictly prohibit the intentional venting of regulated refrigerants
and mandate the use of certified recovery equipment and DOT-approved recovery tanks.
