NEVADA C-21B AIR-CONDITIONING CONTRACTOR EXAM
Nevada C-21B Air Conditioning Contractor licensure
Updated Questions & Answers With Rationale
A+ Graded| Brand New Release!
This comprehensive practice exam consists of 250 multiple-choice questions designed to
assess the knowledge and skills required for the Nevada C-21B Air Conditioning
Contractor license. The C-21B is a limited residential classification issued by the Nevada
State Contractors Board (NSCB) that authorizes the installation, repair, service, and
maintenance of residential air conditioning systems, including related ductwork and
humidity/thermostatic controls. The C-21B is restricted to residential work only and
does not permit commercial HVAC or refrigeration projects. The trade exam is a 60-
question, open-book assessment administered by PSI. A minimum score of 70% is
required to pass, and candidates must also pass the Construction Management Survey
(CMS) exam to obtain a valid Nevada contractor license.
DOMAINS COVERED:
1. Nevada Licensing and Business Law (~10%)
2. HVAC Fundamentals and Thermodynamics (~13%)
3. System Design and Load Calculations (~13%)
4. Mechanical Codes and Standards (~13%)
5. Refrigeration and Refrigerant Management (~10%)
6. Electrical Systems and Controls (~10%)
7. Heating Systems (~10%)
8. Installation, Maintenance, and Repair (~10%)
9. Safety and Project Management (~10%)
Question 1
What is the primary purpose of a disconnect switch within sight of an air
conditioning unit?
,A. To act as a regular operating control
B. To de-energize the unit for safe servicing
C. To protect the compressor from low voltage
D. To reset the circuit breaker remotely
Correct Answer: B
Rationale: The NEC requires a disconnect within sight of the appliance to allow
service personnel to safely lock out the power source.
Question 2
A capacitor labeled "35/5 uF 440V" is typically a:
A. Start Capacitor
B. Run Capacitor
C. Dual Run Capacitor
D. Booster Capacitor
Correct Answer: C
Rationale: The dual rating (35uF and 5uF) indicates it serves two functions, typically
for the compressor (35uF) and the condenser fan motor (5uF).
Question 3
The locking, rotary compressor used in most modern residential AC systems is
powered by:
,A. Single-Phase AC Current
B. Three-Phase AC Current
C. Direct Current (DC)
D. Split-Phase DC Current
Correct Answer: A
Rationale: Residential power is almost exclusively single-phase. Three-phase is more
common in large commercial applications.
Question 4
If a technician measures 0 ohms across a fuse with the power OFF, it indicates the
fuse is:
A. Blown
B. Good
C. Requires more testing
D. The wrong type
Correct Answer: B
Rationale: 0 ohms indicates continuity, meaning the circuit inside the fuse is complete
and unbroken.
Question 5
The LRA (Locked Rotor Amps) of a compressor motor represents:
, A. The normal running current
B. The current draw when the rotor is unable to turn
C. The current at the moment of start
D. The maximum continuous current
Correct Answer: B
Rationale: LRA is the very high current drawn when the motor is energized but not
rotating, which can be 5-7 times higher than the RLA.
Question 6
A potential relay is used to:
A. Protect the compressor from high pressure
B. Remove the start capacitor from the circuit once the motor reaches about 75% of
its rated speed
C. Control the low-voltage thermostat circuit
D. Sense low refrigerant charge
Correct Answer: B
Rationale: Potential relays use back EMF (electromotive force) generated by the
motor itself to open the circuit to the start capacitor.
Question 7
The minimum working clearance in front of a 240V electrical panel, as per NEC, is:
Nevada C-21B Air Conditioning Contractor licensure
Updated Questions & Answers With Rationale
A+ Graded| Brand New Release!
This comprehensive practice exam consists of 250 multiple-choice questions designed to
assess the knowledge and skills required for the Nevada C-21B Air Conditioning
Contractor license. The C-21B is a limited residential classification issued by the Nevada
State Contractors Board (NSCB) that authorizes the installation, repair, service, and
maintenance of residential air conditioning systems, including related ductwork and
humidity/thermostatic controls. The C-21B is restricted to residential work only and
does not permit commercial HVAC or refrigeration projects. The trade exam is a 60-
question, open-book assessment administered by PSI. A minimum score of 70% is
required to pass, and candidates must also pass the Construction Management Survey
(CMS) exam to obtain a valid Nevada contractor license.
DOMAINS COVERED:
1. Nevada Licensing and Business Law (~10%)
2. HVAC Fundamentals and Thermodynamics (~13%)
3. System Design and Load Calculations (~13%)
4. Mechanical Codes and Standards (~13%)
5. Refrigeration and Refrigerant Management (~10%)
6. Electrical Systems and Controls (~10%)
7. Heating Systems (~10%)
8. Installation, Maintenance, and Repair (~10%)
9. Safety and Project Management (~10%)
Question 1
What is the primary purpose of a disconnect switch within sight of an air
conditioning unit?
,A. To act as a regular operating control
B. To de-energize the unit for safe servicing
C. To protect the compressor from low voltage
D. To reset the circuit breaker remotely
Correct Answer: B
Rationale: The NEC requires a disconnect within sight of the appliance to allow
service personnel to safely lock out the power source.
Question 2
A capacitor labeled "35/5 uF 440V" is typically a:
A. Start Capacitor
B. Run Capacitor
C. Dual Run Capacitor
D. Booster Capacitor
Correct Answer: C
Rationale: The dual rating (35uF and 5uF) indicates it serves two functions, typically
for the compressor (35uF) and the condenser fan motor (5uF).
Question 3
The locking, rotary compressor used in most modern residential AC systems is
powered by:
,A. Single-Phase AC Current
B. Three-Phase AC Current
C. Direct Current (DC)
D. Split-Phase DC Current
Correct Answer: A
Rationale: Residential power is almost exclusively single-phase. Three-phase is more
common in large commercial applications.
Question 4
If a technician measures 0 ohms across a fuse with the power OFF, it indicates the
fuse is:
A. Blown
B. Good
C. Requires more testing
D. The wrong type
Correct Answer: B
Rationale: 0 ohms indicates continuity, meaning the circuit inside the fuse is complete
and unbroken.
Question 5
The LRA (Locked Rotor Amps) of a compressor motor represents:
, A. The normal running current
B. The current draw when the rotor is unable to turn
C. The current at the moment of start
D. The maximum continuous current
Correct Answer: B
Rationale: LRA is the very high current drawn when the motor is energized but not
rotating, which can be 5-7 times higher than the RLA.
Question 6
A potential relay is used to:
A. Protect the compressor from high pressure
B. Remove the start capacitor from the circuit once the motor reaches about 75% of
its rated speed
C. Control the low-voltage thermostat circuit
D. Sense low refrigerant charge
Correct Answer: B
Rationale: Potential relays use back EMF (electromotive force) generated by the
motor itself to open the circuit to the start capacitor.
Question 7
The minimum working clearance in front of a 240V electrical panel, as per NEC, is:
