Nevada (NV) C-21B Air Conditioning Contractor Practice
Exam 2026/2027 | 2 Full Versions, 200 Questions with
Correct Answers & Detailed Rationales | Instant
Download PDF
The Nevada C-21B Air Conditioning Contractor exam is a trade assessment administered by
PSI on behalf of the Nevada State Contractors Board (NSCB). It is a key requirement, along
with the Construction Management Survey (CMS) exam, to obtain a valid contrac tor's license
in the state
Core Exam Domains
The exam content is divided into five main areas, covering the full lifecycle of HVAC systems.
The approximate weight of each section is as follows:
• General Knowledge & Safety (25%) : Covers thermodynamics, Uniform Mechanical
Code (UMC) standards, OSHA safety regulations, and pressure testing procedures.
• Systems & Equipment (25%) : Focuses on the installation and operation of A/C units,
heat pumps, furnaces, and ventilation systems.
• Piping & Refrigerants (20%) : Includes refrigerant handling (EPA 608 certification is a
key topic), gas piping, and condensate drainage.
• Load Calculations (15%) : Requires using Manual J, S, and D to determine proper
cooling/heating requirements and duct sizing.
• Controls (15%) : Covers low-voltage wiring, thermostats, and electrical safety and
troubleshooting.
,Nevada (NV) C-21B Air Conditioning Contractor Practice Exam
Version 1 (Questions 1-20)
1. According to the Uniform Mechanical Code (UMC), what is the minimum clearance
required in front of a furnace control side for service and inspection?
A. 18 inches
B. 24 inches
C. 30 inches
D. 36 inches
Answer: C. 30 inches
Rationale: To ensure technician safety and proper tool maneuverability, the UMC
requires a minimum of 30 inches of working space in front of the control side of the
equipment. This allows for the safe removal of burners, blowers, and controls without
obstruction.
2. When installing a condensate drain line for a high-efficiency furnace, what is the
minimum slope required to ensure proper drainage?
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
Answer: B. 1/4 inch per foot
Rationale: Gravity-fed condensate lines must maintain a minimum slope of 1/4 inch per
foot (2% grade). If the slope is too shallow, biofilm (slime) can build up, leading to clogs,
water damage, and system shutdowns via the float switch.
3. In a heat pump system, the "Reversing Valve" is typically energized in which mode for
most manufacturers?
A. Heating
B. Cooling
C. Defrost only
D. Emergency heat only
Answer: B. Cooling
Rationale: While some brands vary, the industry standard is for the reversing valve (O-
terminal) to be energized in the cooling mode. This allows the system to fail-safe into the
heating mode during winter if the solenoid coil fails.
4. What is the maximum permitted length of a flexible air duct (flex duct) according to
standard Nevada energy conservation codes?
, A. 5 feet
B. 10 feet
C. 14 feet
D. 25 feet
Answer: C. 14 feet
Rationale: While some jurisdictions allow longer runs, the general standard for efficiency
is to limit flexible ducts to 14 feet. Excessively long flex duct runs significantly increase
static pressure and reduce airflow due to the internal friction of the wire helix.
5. According to the International Fuel Gas Code (IFGC), a gas shut-off valve must be located
within how many feet of the appliance it serves?
A. 3 feet
B. 6 feet
C. 10 feet
D. Within the same room, no distance limit
Answer: B. 6 feet
Rationale: The shut-off valve must be in the same room and within 6 feet of the
appliance. This ensures that in the event of a gas leak or fire at the unit, a technician or
occupant can quickly and safely isolate the fuel source.
6. What is the primary purpose of a "Subcooling" measurement when charging a system
with a Thermostatic Expansion Valve (TXV)?
A. To check the evaporator's efficiency.
B. To ensure the condenser is clean.
C. To verify the liquid line has a solid column of refrigerant.
D. To measure the temperature of the suction line.
Answer: C. To verify the liquid line has a solid column of refrigerant.
Rationale: Subcooling measures how much the liquid refrigerant is cooled below its
saturation temperature. A proper subcooling reading confirms that the condenser is
condensing all the refrigerant and that a solid column of liquid is reaching the TXV,
preventing flash gas.
7. What is the minimum SEER rating required for a new residential central air conditioner in
Nevada?
A. 10 SEER
B. 13 SEER
C. 14 SEER
D. 16 SEER
Answer: C. 14 SEER
, Rationale: Federal minimum efficiency standards require new residential central air
conditioners to be at least 14 SEER. Nevada follows these federal guidelines for new
installations.
8. What is the purpose of a crankcase heater on a compressor?
A. To warm the compressor oil before startup.
B. To prevent refrigerant migration to the compressor during the off cycle.
C. To increase the heating capacity of the heat pump.
D. To cool the compressor during operation.
Answer: B. To prevent refrigerant migration to the compressor during the off cycle.
Rationale: A crankcase heater keeps the compressor oil warm to prevent liquid
refrigerant from migrating and mixing with the oil during the off cycle. This prevents oil
dilution and potential compressor slugging on startup.
9. What is the primary function of a low-voltage transformer in an HVAC system?
A. To increase the voltage for the compressor.
B. To step down 240V/120V to 24V for the control circuit.
C. To convert AC power to DC power.
D. To regulate the fan speed.
Answer: B. To step down 240V/120V to 24V for the control circuit.
Rationale: The transformer reduces the incoming line voltage to 24 volts, which is used
to safely power the thermostat, contactors, and other low-voltage control components.
10. When brazing copper refrigerant lines, what gas is typically used to purge the lines and
prevent oxidation?
A. Oxygen
B. Acetylene
C. Nitrogen
D. Carbon Dioxide
Answer: C. Nitrogen
Rationale: Nitrogen is used to purge the lines during brazing. This prevents the
formation of copper oxide (scale) inside the tubing, which can later flake off and clog the
TXV, filter drier, or compressor.
11. What is the standard airflow requirement per ton of cooling for a residential air
conditioning system?
A. 200 CFM
B. 400 CFM
C. 600 CFM
D. 800 CFM
Exam 2026/2027 | 2 Full Versions, 200 Questions with
Correct Answers & Detailed Rationales | Instant
Download PDF
The Nevada C-21B Air Conditioning Contractor exam is a trade assessment administered by
PSI on behalf of the Nevada State Contractors Board (NSCB). It is a key requirement, along
with the Construction Management Survey (CMS) exam, to obtain a valid contrac tor's license
in the state
Core Exam Domains
The exam content is divided into five main areas, covering the full lifecycle of HVAC systems.
The approximate weight of each section is as follows:
• General Knowledge & Safety (25%) : Covers thermodynamics, Uniform Mechanical
Code (UMC) standards, OSHA safety regulations, and pressure testing procedures.
• Systems & Equipment (25%) : Focuses on the installation and operation of A/C units,
heat pumps, furnaces, and ventilation systems.
• Piping & Refrigerants (20%) : Includes refrigerant handling (EPA 608 certification is a
key topic), gas piping, and condensate drainage.
• Load Calculations (15%) : Requires using Manual J, S, and D to determine proper
cooling/heating requirements and duct sizing.
• Controls (15%) : Covers low-voltage wiring, thermostats, and electrical safety and
troubleshooting.
,Nevada (NV) C-21B Air Conditioning Contractor Practice Exam
Version 1 (Questions 1-20)
1. According to the Uniform Mechanical Code (UMC), what is the minimum clearance
required in front of a furnace control side for service and inspection?
A. 18 inches
B. 24 inches
C. 30 inches
D. 36 inches
Answer: C. 30 inches
Rationale: To ensure technician safety and proper tool maneuverability, the UMC
requires a minimum of 30 inches of working space in front of the control side of the
equipment. This allows for the safe removal of burners, blowers, and controls without
obstruction.
2. When installing a condensate drain line for a high-efficiency furnace, what is the
minimum slope required to ensure proper drainage?
A. 1/8 inch per foot
B. 1/4 inch per foot
C. 1/2 inch per foot
D. 1 inch per foot
Answer: B. 1/4 inch per foot
Rationale: Gravity-fed condensate lines must maintain a minimum slope of 1/4 inch per
foot (2% grade). If the slope is too shallow, biofilm (slime) can build up, leading to clogs,
water damage, and system shutdowns via the float switch.
3. In a heat pump system, the "Reversing Valve" is typically energized in which mode for
most manufacturers?
A. Heating
B. Cooling
C. Defrost only
D. Emergency heat only
Answer: B. Cooling
Rationale: While some brands vary, the industry standard is for the reversing valve (O-
terminal) to be energized in the cooling mode. This allows the system to fail-safe into the
heating mode during winter if the solenoid coil fails.
4. What is the maximum permitted length of a flexible air duct (flex duct) according to
standard Nevada energy conservation codes?
, A. 5 feet
B. 10 feet
C. 14 feet
D. 25 feet
Answer: C. 14 feet
Rationale: While some jurisdictions allow longer runs, the general standard for efficiency
is to limit flexible ducts to 14 feet. Excessively long flex duct runs significantly increase
static pressure and reduce airflow due to the internal friction of the wire helix.
5. According to the International Fuel Gas Code (IFGC), a gas shut-off valve must be located
within how many feet of the appliance it serves?
A. 3 feet
B. 6 feet
C. 10 feet
D. Within the same room, no distance limit
Answer: B. 6 feet
Rationale: The shut-off valve must be in the same room and within 6 feet of the
appliance. This ensures that in the event of a gas leak or fire at the unit, a technician or
occupant can quickly and safely isolate the fuel source.
6. What is the primary purpose of a "Subcooling" measurement when charging a system
with a Thermostatic Expansion Valve (TXV)?
A. To check the evaporator's efficiency.
B. To ensure the condenser is clean.
C. To verify the liquid line has a solid column of refrigerant.
D. To measure the temperature of the suction line.
Answer: C. To verify the liquid line has a solid column of refrigerant.
Rationale: Subcooling measures how much the liquid refrigerant is cooled below its
saturation temperature. A proper subcooling reading confirms that the condenser is
condensing all the refrigerant and that a solid column of liquid is reaching the TXV,
preventing flash gas.
7. What is the minimum SEER rating required for a new residential central air conditioner in
Nevada?
A. 10 SEER
B. 13 SEER
C. 14 SEER
D. 16 SEER
Answer: C. 14 SEER
, Rationale: Federal minimum efficiency standards require new residential central air
conditioners to be at least 14 SEER. Nevada follows these federal guidelines for new
installations.
8. What is the purpose of a crankcase heater on a compressor?
A. To warm the compressor oil before startup.
B. To prevent refrigerant migration to the compressor during the off cycle.
C. To increase the heating capacity of the heat pump.
D. To cool the compressor during operation.
Answer: B. To prevent refrigerant migration to the compressor during the off cycle.
Rationale: A crankcase heater keeps the compressor oil warm to prevent liquid
refrigerant from migrating and mixing with the oil during the off cycle. This prevents oil
dilution and potential compressor slugging on startup.
9. What is the primary function of a low-voltage transformer in an HVAC system?
A. To increase the voltage for the compressor.
B. To step down 240V/120V to 24V for the control circuit.
C. To convert AC power to DC power.
D. To regulate the fan speed.
Answer: B. To step down 240V/120V to 24V for the control circuit.
Rationale: The transformer reduces the incoming line voltage to 24 volts, which is used
to safely power the thermostat, contactors, and other low-voltage control components.
10. When brazing copper refrigerant lines, what gas is typically used to purge the lines and
prevent oxidation?
A. Oxygen
B. Acetylene
C. Nitrogen
D. Carbon Dioxide
Answer: C. Nitrogen
Rationale: Nitrogen is used to purge the lines during brazing. This prevents the
formation of copper oxide (scale) inside the tubing, which can later flake off and clog the
TXV, filter drier, or compressor.
11. What is the standard airflow requirement per ton of cooling for a residential air
conditioning system?
A. 200 CFM
B. 400 CFM
C. 600 CFM
D. 800 CFM
