10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
The NV-C21 exam has 85 questions and runs 3 hours.
These 10 free NV-C21 questions are organized by exam domain, so you can see how each part of the Nevada C-21 Refrigeration and Air Conditioning Contractor Trade Exam blueprint is tested. Reveal the answer and explanation under each question.
Domain 3: Hangers and Supports
Question 1
Condensation appears only at the hangers of a chilled-water line. Away from the hangers, the insulation jacket is dry and its surface is above the room dew point. At each wet location, a narrow hanger has crushed the soft insulation and torn its vapor retarder. The pipe is not leaking. Which repair corrects the support detail rather than merely concealing the moisture?
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Correct answer: C - Install load-bearing insulation inserts and shields, then restore continuous vapor-retarder seals.
Domain 6: Refrigerants and Refrigeration
Question 2
A walk-in cooler cannot pull down to setpoint. Its evaporator is clear of ice, airflow is normal, and the TXV bulb is secure. Steady readings show low suction pressure, high evaporator-outlet superheat, and adequate liquid subcooling upstream of the filter-drier. A pronounced temperature drop occurs across the drier, with no comparable drop elsewhere in the liquid line. Which single fault best fits the evidence?
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Correct answer: C - A restriction within the liquid-line filter-drier
Domain 7: Load Calculations
Question 3
A commercial cooling-load calculation gives 34,000 Btu/h sensible and 12,000 Btu/h latent at the coincident design condition. Four equipment selections have the net capacities shown below, all evaluated at that same condition with indoor-fan heat accounted for. The specification calls for the lowest total-capacity selection that satisfies both load components. Which selection should be submitted?
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Correct answer: B - 49,000 Btu/h total: 36,000 sensible and 13,000 latent
Domain 9: Controls
Question 4
A contactor will not pull in. The 24-V series control circuit is R → thermostat cooling contact → high-pressure switch → contactor coil → C. The coil and return conductor passed continuity checks with power isolated. During an energized voltage test by a qualified technician, R-to-C measures 24 V, the thermostat contact has essentially zero voltage drop, and the high-pressure switch has 24 V across its contacts. These readings establish that:
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Correct answer: C - The high-pressure switch is open; the measurements do not explain why.
Domain 11: A/C and Heat Pump Equipment
Question 5
An owner reports that a heat pump occasionally releases a white cloud outdoors on cold, damp mornings. During an observed cycle, the compressor continues running, the outdoor fan stops, supplemental indoor heat operates, and frost melts from the outdoor coil. A few minutes later, the outdoor fan and normal heating resume with the coil clear. There is no burning odor or fault indication. What should the contractor recommend after witnessing this sequence?
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Correct answer: D - Leave the settings unchanged; the observed sequence is normal reverse-cycle defrost.
Domain 12: Furnaces and Heaters
Question 6
An induced-draft furnace lights its burners, but the control removes power from the gas valve a few seconds later. Draft proof remains established, inlet and manifold pressures meet the appliance specifications, and flame is visible during the trial. The control requires at least 1.0 microamp DC for flame proof; the measured flame signal is only 0.2 microamp DC. Where should the next diagnostic work be concentrated?
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Correct answer: D - The flame-sensing circuit, including the sensor, its connections, and the burner ground path
Domain 14: Chimneys, Flues and Vents
Question 7
For a furnace replacement, the existing Type B gas vent passes condition, clearance, and applicable minimum-and-maximum capacity checks for the proposed fan-assisted Category I furnace. The furnace instructions permit that vent arrangement. An installer nevertheless proposes replacing it solely because the new furnace has an inducer. How should the reviewer resolve the proposal?
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Correct answer: A - Retain the verified Type B vent; an inducer alone does not determine vent category.
Domain 16: Fuel Systems
Question 8
Size a natural-gas common header and its furnace-only branch by the longest-length method. The header supplies a furnace rated 100,000 Btu/h input and 80,000 Btu/h output, plus a unit heater rated 60,000 Btu/h input. The most remote outlet is 45 developed feet from the delivery point. Gas heating value is 1,000 Btu/ft³.
Applicable iron-pipe capacities in ft³/h, for gas specific gravity 0.60, supply pressure no greater than 0.5 psig, and 0.5-inch-water-column allowable drop:
40-ft row: 1/2 inch = 82; 3/4 inch = 170; 1 inch = 320.
50-ft row: 1/2 inch = 73; 3/4 inch = 151; 1 inch = 285.
What are the smallest permitted nominal sizes for the header and furnace branch, respectively?
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Correct answer: A - 1-inch header; 3/4-inch furnace branch
Question 9
New fuel-gas piping is ready for its required 3-psig nitrogen pressure test. A connected furnace and its individual manual shutoff valve are rated for no more than 0.5 psig. The crew plans to close that manual valve and leave both components attached to the test piping. How must the setup be changed before pressurization?
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Correct answer: B - Disconnect the furnace and manual shutoff valve, then cap the supply piping for testing.
Domain 22: Safety
Question 10
A fixed refrigerant alarm sounds in a machinery room and everyone exits. From outside, a technician samples room air through a remote sampling tube: oxygen is 20.9% and combustible gas reads 0% of the lower flammability limit. The portable meter has no sensor for the refrigerant in use, and the release concentration is unknown. No one needs rescue. What response is appropriate at this point?
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Correct answer: A - Maintain evacuation, prevent re-entry, and activate the site's refrigerant emergency-response plan.