NATE certification: the HVAC credential employers pay for

25 questions · Fundamentals: electricity, heat & science. Pick an answer for each, then check. Explanations cite the rule each question tests.

1. 1. A circuit has 120V applied across a 20Ω heater element. The current is:

   2.4A6A12A0.17A

2. 2. Power consumed by that same element is:

   120W240W720W2,400W

3. 3. In a SERIES circuit, which quantity is the same through every component?

   VoltageCurrentResistancePower

4. 4. In a PARALLEL circuit, which is the same across every branch?

   CurrentVoltageResistanceWattage

5. 5. Adding a second equal resistance in parallel makes total resistance:

   DoubleHalfThe sameZero

6. 6. The typical control-circuit voltage in residential HVAC, supplied by a step-down transformer, is:

   12V DC24V AC48V DC120V AC

7. 7. A transformer rated 40 VA at 24V secondary can safely supply about:

   0.6A1.7A4A10A

8. 8. The component that closes the high-voltage circuit to the compressor when the thermostat calls is the:

   CapacitorContactorSequencerLimit switch

9. 9. A run capacitor's job in a PSC motor is to:

   Store energy for power outagesCreate a phase-shifted current in the start winding to produce running torque and efficiencyFilter harmonicsProtect against overload

10. 10. A microfarad meter reads a 35/5 dual capacitor's HERM section at 20 µF. The capacitor is:

    FineFailed/degraded — beyond the ±6% class tolerance from 35 µFOverchargedMiswired

11. 11. Heat always flows:

    From cold to hotFrom a higher-temperature substance to a lower-temperature substanceToward the compressorUpward only

12. 12. Heat transfer through a solid wall (molecule to molecule) is:

    ConvectionRadiationConductionEvaporation

13. 13. One BTU is the heat required to raise:

    1 lb of water 1°F1 gallon of water 1°F1 lb of air 1°F1 kg of water 1°C

14. 14. One ton of refrigeration equals:

    3,412 BTU/h12,000 BTU/h15,000 BTU/h24,000 BTU/h

15. 15. Heat that changes a substance's temperature (measurable with a thermometer) is:

    Latent heatSensible heatSpecific heatSuperheat

16. 16. The heat absorbed when 1 lb of water evaporates (~970 BTU) without temperature change is called:

    Sensible heatLatent heat of vaporizationSuperheatSubcooling

17. 17. Superheat is:

    Any temperature above 100°FSensible heat added to a vapor above its saturation temperatureHeat in the compressorLiquid temperature below saturation

18. 18. Subcooling is:

    Liquid cooled below its saturation temperatureVapor above saturationThe metering-device dropEvaporator frost

19. 19. As the pressure on a refrigerant increases, its saturation (boiling) temperature:

    DecreasesIncreasesStays constantBecomes zero

20. 20. In the basic vapor-compression cycle, refrigerant absorbs heat in the:

    CondenserEvaporatorCompressorReceiver

21. 21. The component that meters high-pressure liquid into the evaporator is the:

    CompressorMetering device (TXV, piston, or capillary tube)AccumulatorReversing valve

22. 22. In a heat pump, the reversing valve:

    Reverses the compressor rotationRedirects refrigerant flow so the indoor coil becomes the condenser in heating modeBypasses the filterControls defrost only

23. 23. Relative humidity is:

    The weight of water in airThe percentage of moisture air holds compared to the maximum it could hold at that temperatureDew pointWet-bulb temperature

24. 24. Wet-bulb temperature is measured to determine:

    Sensible load onlyThe moisture content/latent condition of air (with dry-bulb, it fixes the psychrometric state)Duct leakageRefrigerant charge directly

25. 25. Density of standard air used in airflow formulas corresponds to the constant 1.08 in Q(sensible) = 1.08 × CFM × ΔT. The formula returns:

    WattsSensible BTU/h moved by an airstreamLatent BTU/hTons

25 questions · Applied: airflow, safety, tools & comfort. Pick an answer for each, then check. Explanations cite the rule each question tests.

1. 1. Nominal design airflow across a residential cooling coil is approximately:

   100 CFM per ton400 CFM per ton800 CFM per ton1,200 CFM per ton

2. 2. Static pressure in a duct system is measured with a:

   PsychrometerManometer (or digital pressure gauge) via test portsAnemometerMultimeter

3. 3. Most residential PSC blowers are rated to deliver design airflow at a total external static pressure of about:

   0.1 in w.c.0.5 in w.c.2.0 in w.c.5 psi

4. 4. A dirty filter primarily causes:

   Higher airflowReduced airflow — low suction pressure, coil icing, and possible furnace limit tripsHigher subcooling onlyNo effect

5. 5. A higher MERV rating on a filter means:

   Lower filtration, more airflowHigher particle-capture efficiency, and typically more pressure drop to manageLonger filter lifeBetter odors

6. 6. Duct leakage on the RETURN side of a system in an attic tends to:

   Improve efficiencyPull hot, dirty attic air into the system, raising load and harming air qualityCool the atticIncrease static only

7. 7. Human thermal comfort in conditioned spaces generally corresponds to relative humidity between about:

   10–20%30–60%70–90%Exactly 50%

8. 8. Natural gas contains approximately how much heat per cubic foot?

   500 BTU1,000 BTU2,500 BTU10,000 BTU

9. 9. A furnace's AFUE rating expresses:

   AirflowThe percentage of fuel energy converted to useful heat over a seasonSound levelGas pressure

10. 10. The safety control that shuts a furnace down when supply-air temperature is too high is the:

    Flame rollout switch onlyHigh-limit switchPressure switchThermocouple

11. 11. In a condensing (90%+) furnace, the draft inducer pressure switch proves:

    Gas pressureThat combustion venting/draft is established before ignition is allowedBlower speedFilter condition

12. 12. Carbon monoxide is dangerous because it is:

    Visible and pungentColorless, odorless, and produced by incomplete combustionHeavier than air onlyFlammable at 1%

13. 13. Before working inside a condenser's electrical section, the technician should:

    Rely on the thermostat being offOpen the disconnect, verify absence of voltage with a meter, and discharge/verify capacitors safelyWork quicklyRemove only the fan

14. 14. The proper PPE when brazing refrigerant lines includes:

    SunglassesShaded eye protection, gloves, fire-resistant practice (and a fire extinguisher nearby); flow nitrogen through the pipeEarplugs onlyNone if quick

15. 15. A nitrogen cylinder must always be used with:

    A hose directly to the systemA pressure regulator (and secured upright) — full cylinders run ~2,000+ psiA torchAn open valve

16. 16. When lifting equipment, the safe practice is:

    Bend at the waistLift with the legs, keep the load close, and get help or use equipment for heavy itemsTwist while liftingAlways lift alone

17. 17. An extension ladder set against a wall should follow the:

    2:1 rule4:1 rule — base out 1 ft for every 4 ft of working height, with 3 ft extending past the landing6:1 ruleNo rule

18. 18. To measure current draw of a running compressor without breaking the circuit, use a:

    MegohmmeterClamp-on ammeter around one conductorWattmeter in seriesVoltmeter across the contactor

19. 19. Voltage is measured with the meter connected:

    In series with the loadIn parallel (across) the load or sourceAround the wireOnly with power off

20. 20. An ohmmeter or continuity test must only be used:

    On live circuitsWith the circuit de-energized (and the component isolated)During startupOn capacitors while charged

21. 21. Refrigerant contact with skin or eyes can cause:

    NothingFrostbite/freeze burns — wear gloves and safety glasses; flush eyes 15 minutes and seek care if exposedOnly irritationBurns from heat

22. 22. In a customer's home, the professional standard before starting diagnostic work is to:

    Start at the condenserExplain what you will check, protect the work area (shoe covers/drop cloth), and confirm the reported symptom with the customerQuote a price firstReplace parts on spec

23. 23. When explaining a repair to a customer, a technician should:

    Use maximum jargonDescribe the problem, the fix, and the cost in plain language, and answer questions honestly — including optionsAvoid the customerUndersell the issue

24. 24. Before condemning a compressor electrically, a technician should verify:

    Nothing — replace itProper voltage at the unit, capacitor health, and winding resistances (C-S-R pattern, no short to ground) with power offOnly the thermostatThe filter

25. 25. The purpose of a defrost cycle on a heat pump in heating mode is to:

    Heat the house fasterTemporarily reverse the cycle to melt frost off the outdoor coil (auxiliary heat covers the indoor side)Cool the compressorTest the reversing valve