Free NCCER HVAC Technician Knowledge Assessment Practice Questions

Sample Practice Questions

Try these 10 sample questions from the NCCER HVAC Technician Knowledge Assessment practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1Before servicing an HVAC unit with more than one energy source, which sources must the technician control to prevent unexpected startup?

   1. A.The thermostat control circuit alone.
   2. B.The equipment's hazardous energy sources.Correct answer: B
   3. C.The compressor branch circuit alone.
   4. D.The blower motor branch circuit alone.

   Explanation: OSHA states, "Energy sources including electrical, mechanical, hydraulic, pneumatic, chemical, thermal, or other sources in machines and equipment can be hazardous to workers." For a unit with more than one source, controlling only one branch or its thermostat can leave another hazardous source available.

   Reference: OSHA Control of Hazardous Energy overview — What is hazardous energy?

2. 2For a copper-to-copper refrigerant-line braze using a phosphorus-bearing Sil-Fos filler, what is the separate paste-flux requirement described by the filler manufacturer?

   1. A.Apply paste flux to both copper surfaces
   2. B.Apply paste flux only to the fitting
   3. C.No separate paste flux is needed for this pairingCorrect answer: C
   4. D.Apply paste flux after the joint cools

   Explanation: Lucas Milhaupt says, "With Sil-Fos, you do not need paste flux, because Sil-Fos alloys contain a fluxing agent." This applies to the specified copper-to-copper pairing; it must not be generalized to copper-to-brass joints.

   Reference: Lucas Milhaupt Brazing Components for Refrigeration — Alloy Selection, Copper-to-copper

3. 3What does a gas furnace's AFUE percentage compare?

   1. A.Space heat delivered with fuel entering the furnaceCorrect answer: A
   2. B.Flue-gas heat carried away with fuel entering the furnace
   3. C.Blower electrical input with space heat delivered
   4. D.Steady-state burner output with nameplate fuel input

   Explanation: DOE defines AFUE as "the amount of fuel converted to space heat in proportion to the amount of fuel entering the boiler or furnace; expressed as a percentage." It is a fuel-to-space-heat efficiency measure, not an airflow or pressure ratio.

   Reference: DOE Energy Renovations HVAC Guide — Furnace and Boiler Equipment Efficiency, p. 7

4. 4A stationary refrigeration system shows a pressure drop on a standing test. Which additional test can locate the leak?

   1. A.Bubble testing the suspected jointCorrect answer: A
   2. B.Repeating only the standing pressure test
   3. C.Reading the receiver level again
   4. D.Comparing a charging chart alone

   Explanation: EPA explains that a leak inspection locates refrigerant leaks and lists "bubble tests" among locating methods. It distinguishes pressure decay and charging charts, which can show a problem but do not locate it.

   Reference: EPA Refrigerant Management Q&A for Section 608 Technicians — Questions on Servicing Appliances with 50 or More Pounds, leak inspection

5. 5A gas furnace repeatedly shuts its burners off on a high-temperature limit and has a heavily clogged return-air filter. What causal condition should be addressed first?

   1. A.Restricted airflow across the heat exchangerCorrect answer: A
   2. B.Excessive airflow cooling the heat exchanger
   3. C.A normal thermostat cycle at its setpoint
   4. D.A low-temperature limit responding to cold supply air

   Explanation: Carrier says, "A furnace limit switch typically trips due to severely restricted airflow across the heat exchanger, which causes the internal temperature of the furnace to spike beyond safe operating levels." The clogged return filter directly supports checking and correcting that restriction.

   Reference: Carrier Furnace Limit Switch Guide — What Causes a Furnace Limit Switch to Trip?

6. 6Why does Copeland specify POE rather than mineral oil for the HFC refrigerants in its refrigeration fundamentals?

   1. A.Mineral oil is more polar and miscible with HFCs.
   2. B.POE's polarity makes it miscible with HFCs.Correct answer: B
   3. C.POE keeps HFC vapor from migrating into crankcase oil.
   4. D.Mineral oil becomes miscible with HFCs after evacuation.

   Explanation: Copeland states, "The result is that mineral oils are not miscible with the HFC refrigerants. Polyol Ester (POE) lubricants are more polar than the mineral oils. This polarity of the POE and HFCs make the two miscible". The miscibility difference follows from POE's polarity, not from changing the oil through evacuation.

   Reference: Copeland Fundamentals of Refrigeration — Lubricants and HFC refrigerants, p. 33

7. 7In a primary-secondary chilled-water pumping arrangement, which pumps circulate water through the chiller itself?

   1. A.The primary pumps.Correct answer: A
   2. B.The secondary pumps.
   3. C.The condenser-water tower pumps.
   4. D.The chilled-water distribution booster pumps.

   Explanation: The DOE guide states, "In primary-secondary systems, the primary pumps circulate chilled water through the chiller(s), and the secondary pumps draw from that loop to circulate chilled water to the air handler(s)." Thus the primary pumps serve the chiller loop.

   Reference: DOE Asset Score Upgrade Guide: Chilled Water Systems — Upgrade Cooling Plant Pumping System to Constant Primary - Variable Secondary Pumping System

8. 8An AprilAire evaporative humidifier's water solenoid clicks on a humidity call, but no water flows. What should the technician investigate first?

   1. A.An obstruction in the water path, including the strainer or orifice.Correct answer: A
   2. B.An absent humidity call despite the solenoid click.
   3. C.A closed fan circuit despite verified airflow.
   4. D.A low thermostat setting despite a humidity call.

   Explanation: AprilAire explains, "If the water solenoid valve does make a click sound when the humidity level is increased but no water flows this indicates the water flow is obstructed." It then identifies the orifice and in-line strainer as checks, so the click directs attention to water flow.

   Reference: AprilAire Frequently Asked Questions — Why is there no water coming out of my AprilAire Evaporative Humidifier?

9. 9An office has an identifiable indoor pollutant source. Which indoor-air-quality strategy addresses the pollutant at its origin?

   1. A.Increase recirculation through the existing ducts.
   2. B.Manage the source by removing or isolating it.Correct answer: B
   3. C.Increase outdoor-air ventilation around the source.
   4. D.Increase filtration of the mixed return air.

   Explanation: EPA identifies source management as a primary strategy: "manage the sources of pollutants either by removing them from the building or isolating them from people". Ventilation and filtration may reduce exposure or concentration, but the question asks for control at the origin.

   Reference: EPA An Office Building Occupant's Guide to Indoor Air Quality — Factors that Contribute to Indoor Air Quality

10. 10In a commercial refrigerated case, why does a heavy frost layer on the evaporator coil reduce cooling performance?

    1. A.It increases thermal resistance and obstructs airflow.Correct answer: A
    2. B.It decreases thermal resistance while obstructing airflow.
    3. C.It increases airflow while insulating the coil.
    4. D.It improves both airflow and heat transfer across the coil.

    Explanation: DOE states, "The frost reduces cooling performance by increasing the thermal resistance to heat transfer from the coil to the air, and by obstructing airflow." Both the heat-transfer barrier and blocked airflow explain the loss of capacity.

    Reference: DOE Commercial Refrigeration Equipment Technical Support Document — Section 3.3.1.11, Defrost Mechanisms, p. 3-34