CSLB HVAC (C-20) Trade Practice Test

Sample practice questions

A few real questions from this free bank, with full explanations. Use the practice tool above for the whole set.

1. 1. Load & Design

   In residential load calculations, what does an ACCA Manual J procedure primarily determine?

   • a.The size and gauge of the supply ductwork
   • b.The building's heating and cooling loads
   • c.The refrigerant charge for the condenser
   • d.The electrical service size for the panel

   Answer: b

   Explanation: Manual J is the industry-standard residential load calculation method. It estimates the sensible and latent heating and cooling loads by accounting for construction, insulation, windows, orientation, infiltration, and local design temperatures. Equipment is then selected to match those calculated loads.

   Source: California Energy Code (Title 24)

2. 2. Installation

   Why should supply and return ducts be sealed with mastic or listed tape at joints?

   • a.To increase the gas supply pressure at the burner
   • b.To stop leakage that wastes energy and airflow
   • c.To hold refrigerant inside the duct system
   • d.To help support the weight of the furnace

   Answer: b

   Explanation: Sealing duct joints with mastic or UL-listed tape prevents conditioned air from leaking into unconditioned spaces, which wastes energy and starves rooms of airflow. Leaky returns can also draw in dust or combustion products. California energy standards require duct sealing and testing.

3. 3. Service & Troubleshooting

   SEER (or SEER2) is a rating that describes what?

   • a.The seasonal heating efficiency of a gas furnace
   • b.Seasonal cooling efficiency of the equipment
   • c.The refrigerant type used in the system
   • d.The measured duct leakage rate at test

   Answer: b

   Explanation: SEER, and the updated SEER2, express the seasonal cooling output divided by the electrical energy input, so a higher number means greater cooling efficiency. It is used to compare and select air conditioners and heat pumps. California energy standards set minimum SEER values.

4. 4. Load & Design

   How does duct located in a vented attic affect a Manual J cooling load?

   • a.It reduces the load because attic air pre-cools the supply
   • b.It affects only the heating load, not the cooling load
   • c.It has no effect on the load, because the ducts are inside the building footprint
   • d.It adds conduction gain and leakage loss that must be included in the load

   Answer: d

   Explanation: Ducts in an unconditioned attic gain heat through the insulation and lose conditioned air through leaks, and Manual J includes both as duct load. Being under the roofline is not the same as being inside the thermal envelope. Attic air in summer is far hotter than supply air, so it heats rather than pre-cools. And the penalty applies in both seasons, since the attic is also cold on a winter design morning.

5. 5. Load & Design

   During design you find the return grille face velocity will be about 800 feet per minute. What is the likely outcome?

   • a.Objectionable noise at the grille and elevated return static
   • b.Improved mixing that reduces temperature stratification in the room
   • c.Lower static pressure because the air moves through quickly
   • d.Excellent filtration because dust is captured at high velocity

   Answer: a

   Explanation: Return grilles are normally kept in the range of a few hundred feet per minute, and 800 FPM produces roar and a large pressure drop. High velocity does not improve filtration; it increases the pressure drop across the media and can drive dust deeper into it. Static pressure rises rather than falls when air is forced through a small free area. And mixing is a supply-side diffuser function, not a return-grille one.

6. 6. Installation

   What is the correct arrangement for a sediment trap at a gas furnace?

   • a.A horizontal extension of pipe upstream of the shutoff valve
   • b.A flexible connector looped below the appliance inlet
   • c.A capped vertical leg downstream of the shutoff and ahead of the appliance
   • d.A capped tee installed above the gas valve inlet

   Answer: c

   Explanation: The trap is a tee with a capped drop leg placed after the shutoff and before the appliance, so debris and moisture fall out of the gas stream by gravity. A horizontal extension gives particles no place to settle. A leg above the valve inlet works against gravity and traps nothing. And a looped flexible connector is not a sediment trap and may violate the connector's listing.

7. 7. Installation

   A new furnace is installed and the temperature rise measures 30 F against a rating plate range of 40 to 70 F. What adjustment is appropriate?

   • a.Reduce blower speed until the rise falls inside the listed range
   • b.Increase the manifold gas pressure above the rated value
   • c.Replace the limit switch with one rated for a lower setpoint
   • d.Add restriction at the return duct to raise the system static pressure

   Answer: a

   Explanation: Too low a rise means the blower is moving more air than the burner output warrants, so slowing the blower brings the rise into range. Overfiring the burner past its rated manifold pressure is unsafe and voids the listing. Deliberately restricting the return raises static and stresses the blower rather than properly setting speed. And changing the limit switch masks an airflow setting problem while removing a safety margin.

8. 8. Refrigeration

   How does a compressor's discharge temperature respond to very high suction superheat?

   • a.It stays constant, because the compression ratio governs it entirely
   • b.It rises, because hotter suction gas enters the compression stroke
   • c.It falls, because thinner vapor carries less heat
   • d.It rises only if the condenser is also dirty

   Answer: b

   Explanation: Return gas temperature is one of the two main inputs to discharge temperature, so hot suction vapor produces very hot discharge gas that can break down oil. Lower vapor density reduces mass flow but does not cool the discharge. Compression ratio matters but does not act alone. And the effect appears with a clean condenser as well, since it originates on the suction side.

9. 9. Service & Troubleshooting

   Which instrument gives the most direct measurement of the air a supply register is actually delivering?

   • a.An infrared thermometer aimed at the grille face
   • b.A digital manometer at the supply plenum
   • c.An anemometer held in the center of the duct
   • d.A powered flow hood placed over the register

   Answer: d

   Explanation: A flow hood captures the entire discharge and reports CFM at that outlet directly. A single anemometer reading in the middle of a duct gives a velocity at one point, which must be traversed and converted. A manometer measures pressure, not volume. And an infrared thermometer reads surface temperature, which says nothing about airflow.

10. 10. Safety & Codes

    Why does a residential HVAC change-out generally require a permit and inspection even when the new equipment matches the old?

    • a.Because the work is regulated construction affecting life safety and energy compliance
    • b.Because the utility requires a permit before restoring gas service
    • c.Because permits are what establish the contractor's warranty obligations
    • d.Because inspections determine the equipment's efficiency rating

    Answer: a

    Explanation: Combustion venting, electrical connections, and energy compliance all bear on occupant safety, which is why the jurisdiction reviews and inspects the work. Warranty obligations arise from the contract and the manufacturer, not from the permit. Gas service is not routinely shut off and restored for a change-out. And efficiency ratings are established by laboratory testing, not by a field inspector.