CSLB General Building (B) Trade Practice Test
Frequently asked questions
How many CSLB HVAC (C-20) Trade practice questions are here?+
A full bank of original CSLB HVAC (C-20) Trade practice questions across the official content areas, weighted like the real exam, with explanations. Free, no signup.
What is the CSLB HVAC (C-20) Trade exam like?+
About 100 questions, 210 minutes, and you need 72% to pass. Practice by topic here, then take the full timed mock exam to gauge readiness.
Are these the real exam questions?+
No. Every question is 100% original, written from public primary sources with explanations. We never copy real exam questions or paid prep material.
Can I study in Chinese or Spanish?+
PrepPass practice is in English, 中文 and Español. The official exam is in English — switch the question language to English any time to rehearse the exact terminology you'll see on test day.
Sample practice questions
A few real questions from this free bank, with full explanations. Use the practice tool above for the whole set.
- 1. Load & Design
In residential load calculations, what does an ACCA Manual J procedure primarily determine?
- a.The size and gauge of supply ductwork
- b.The heating and cooling loads of a building based on its construction and climate
- c.The refrigerant charge required 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. Load & Design
Under the California Mechanical Code, when is a permit generally required for HVAC work?
- a.Only for commercial buildings
- b.Only when replacing a thermostat
- c.When installing, altering, or replacing mechanical equipment such as a furnace or air conditioner
- d.Never for residential work
Answer: c
Explanation: The CMC and local jurisdictions require a mechanical permit for installing, altering, or replacing regulated equipment like furnaces, air conditioners, and ductwork. Permits trigger inspection to verify code-compliant, safe installation. Minor maintenance such as filter changes does not require a permit.
Source: 2022 California Mechanical Code (CMC)
- 3. Installation
What is the primary purpose of providing combustion air to a gas-fired furnace?
- a.To cool the electronic controls
- b.To supply oxygen for complete and safe fuel combustion
- c.To increase supply air temperature
- d.To reduce refrigerant pressure
Answer: b
Explanation: A gas furnace needs adequate combustion air so the burner receives enough oxygen for complete combustion. Insufficient air causes incomplete combustion, producing carbon monoxide and sooting. The CMC specifies required openings or ducts based on the appliance input and the confining space.
Source: 2022 California Mechanical Code (CMC)
- 4. Installation
In a split-system heat pump, the outdoor coil functions as the condenser during which mode?
- a.Heating mode
- b.Defrost mode
- c.Cooling mode
- d.Emergency heat mode
Answer: c
Explanation: In cooling mode the outdoor coil rejects heat and acts as the condenser, while the indoor coil absorbs heat as the evaporator. In heating mode the reversing valve swaps these roles. Understanding this reversal is key to installing and servicing heat pumps.
- 5. Installation
The condensate drain line from a cooling coil is often fitted with a trap to accomplish what?
- a.Add refrigerant
- b.Prevent air from being pulled through the drain and allow proper condensate flow
- c.Increase blower speed
- d.Filter the return air
Answer: b
Explanation: A properly sized trap on a draw-through coil prevents the blower's negative pressure from either holding water in the pan or pulling air backward through the drain. This allows condensate to flow freely to the drain. The trap depth is based on the unit's static pressure.
- 6. Refrigeration
A thermostatic expansion valve (TXV) controls refrigerant flow into the evaporator to maintain what?
- a.Constant condenser pressure
- b.Constant compressor speed
- c.A relatively constant evaporator superheat
- d.Constant subcooling
Answer: c
Explanation: A TXV modulates refrigerant flow to hold a stable superheat at the evaporator outlet, matching flow to the load. This keeps the coil fed efficiently and protects the compressor from liquid floodback. It responds to the temperature and pressure of the suction line.
- 7. Refrigeration
As a general principle, adding refrigerant charge to a properly running system tends to do what to the low-side pressure?
- a.Lower it significantly
- b.Raise it
- c.Have no effect
- d.Reverse compressor rotation
Answer: b
Explanation: Adding charge generally raises system pressures, including the suction (low-side) pressure, while removing charge lowers them. Technicians interpret these trends together with superheat and subcooling. Charging must be verified against manufacturer targets, not pressure alone.
- 8. Service & Troubleshooting
A typical low-voltage control (thermostat) circuit in residential HVAC operates at what voltage?
- a.120 volts
- b.240 volts
- c.24 volts
- d.480 volts
Answer: c
Explanation: Residential control circuits generally operate at 24 volts AC, supplied by a step-down transformer. The thermostat switches this low voltage to energize relays and contactors. Measuring 24 volts at the appropriate terminals helps confirm control-circuit operation.
- 9. Service & Troubleshooting
A technician measuring compressor amp draw far above the rated load amps (RLA) should suspect what?
- a.A perfectly healthy compressor
- b.A mechanical or electrical problem such as high head pressure or failing windings
- c.An oversized filter
- d.Low thermostat voltage
Answer: b
Explanation: Amp draw well above the nameplate RLA indicates the compressor is overloaded, which can stem from high head pressure, low voltage, or degrading windings. Continued operation risks overheating and failure. The technician investigates head pressure, voltage, and mechanical condition.
- 10. Safety & Codes
The California Mechanical Code (CMC) primarily governs what?
- a.Electrical wiring only
- b.Plumbing fixtures only
- c.The installation of heating, ventilation, air-conditioning, and refrigeration systems
- d.Structural framing
Answer: c
Explanation: The CMC sets the rules for installing mechanical systems including furnaces, air conditioners, ventilation, and refrigeration, covering venting, combustion air, clearances, and equipment access. Electrical work falls under the CEC and plumbing under the CPC. Contractors coordinate across these codes.
Source: 2022 California Mechanical Code (CMC)