Nevada (NV) C-21B Air Conditioning Contractor Practice
Exam 2026 | 2 Full Versions & Answer Keys
Question 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
Explanation: 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.
Question 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
Explanation: 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 shutdown via the float switch.
Question 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
Explanation: While some brands vary (like Rheem/Ruud), the
industry standard (Carrier, Trane, Goodman) 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.
,Question 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
Explanation: 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.
Question 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
Explanation: 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.
Question 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 check for non-condensables.
Answer: C
Explanation: Subcooling is the temperature drop of the liquid
refrigerant below its saturation point. For TXV systems, subcooling
is the preferred charging method because the TXV maintains a
constant superheat. High subcooling ensures no vapor bubbles
(flash gas) enter the TXV, which would reduce its capacity.
Exam 2026 | 2 Full Versions & Answer Keys
Question 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
Explanation: 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.
Question 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
Explanation: 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 shutdown via the float switch.
Question 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
Explanation: While some brands vary (like Rheem/Ruud), the
industry standard (Carrier, Trane, Goodman) 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.
,Question 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
Explanation: 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.
Question 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
Explanation: 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.
Question 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 check for non-condensables.
Answer: C
Explanation: Subcooling is the temperature drop of the liquid
refrigerant below its saturation point. For TXV systems, subcooling
is the preferred charging method because the TXV maintains a
constant superheat. High subcooling ensures no vapor bubbles
(flash gas) enter the TXV, which would reduce its capacity.
