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CSLB C-20 HVAC Contractor practice questions

200 free questions with answers and explanations.

Practice test
  1. 101.A technician arrives at a service call where a system exhibits low suction pressure, high superheat, low subcooling, and reduced cooling capacity. Which condition most likely explains all of these symptoms together?Cooling and Refrigeration
  2. 102.A Manual J load report shows a total cooling load of 30,000 Btu/hr with a calculated Sensible Heat Ratio (SHR) of 0.80. What is the latent cooling load?Planning and Layout
  3. 103.A technician checks a residential AC system and records: liquid line saturation temperature 108°F, liquid line temperature 95°F, superheat 2°F, and head pressure higher than normal for the outdoor ambient temperature. The manufacturer's target subcooling is 10°F. What is the most likely cause of these readings?Cooling and Refrigeration
  4. 104.A mechanical ventilation system delivers a continuous 90 CFM to a bedroom with a total volume of 4,500 cubic feet. What is the air changes per hour (ACH) for this room?Ventilation and Air Distribution
  5. 105.A Manual S equipment selection process for a home in a high-desert California climate zone uses a 1% cooling design temperature of 105°F. The condensing unit's nameplate capacity is rated at standard AHRI test conditions of 95°F outdoor temperature. What must the contractor do to correctly verify equipment capacity at design conditions?Planning and Layout
  6. 106.A homeowner reports a musty odor and headaches when the furnace runs. A technician suspects a cracked heat exchanger. Which safety instrument should be used FIRST to confirm this hazard before disassembling the furnace?Heating Systems
  7. 107.A technician arrives to recover refrigerant from a system whose compressor has burned out and no longer runs. Which recovery method must be used?Cooling and Refrigeration
  8. 108.Under California Title 24 energy standards, what is the minimum insulation R-value typically required for new supply and return ducts installed in an unconditioned attic space?Planning and Layout
  9. 109.A technician installs a new condensing unit and ensures its crankcase heater is energized for 24 hours before the compressor is started. What is the primary purpose of a crankcase heater?Cooling and Refrigeration
  10. 110.A manufacturer's spec sheet lists a packaged air conditioning unit with a cooling capacity of 36,000 Btu/h while drawing 3,000 watts of electrical input at rated test conditions. What is the unit's EER?Cooling and Refrigeration
  11. 111.A confined utility room contains a 100,000 Btu/h furnace and a 40,000 Btu/h water heater. The installer plans to use the single permanent opening method (1 square inch per 3,000 Btu/h) with the opening located within 12 inches of the ceiling, connecting directly to the outdoors. What minimum free area is required for this opening?Heating Systems
  12. 112.A technician measures static pressure on a residential air handler: supply plenum reads +0.28 inches w.c. and return plenum reads -0.32 inches w.c. What is the Total External Static Pressure (TESP)?Ventilation and Air Distribution
  13. 113.On a standard 24-volt thermostat, which terminal is used to energize the indoor blower relay for continuous or fan-only operation?Controls, Electrical and Safety
  14. 114.A technician is charging an R-410A system at 5,000 feet elevation, where local atmospheric pressure is approximately 12.2 psia (about 2.5 psi below the sea-level standard of 14.7 psia). Using a standard sea-level pressure-temperature chart, what correction should be applied to the gauge reading to determine the correct saturation temperature?Cooling and Refrigeration
  15. 115.A supply duct route requires 80 feet of straight duct, three 90-degree elbows each with an equivalent length of 15 feet, and one tee fitting with an equivalent length of 25 feet. What is the Total Effective Length (TEL) used for the friction rate calculation?Planning and Layout
  16. 116.On a standard 24-volt residential thermostat, which terminal wire typically energizes the compressor contactor coil to start cooling?Controls, Electrical and Safety
  17. 117.A technician installs a hard start kit consisting of a start capacitor and relay on a single-phase compressor that struggles to start under high head pressure. What is the primary purpose of this device?Cooling and Refrigeration
  18. 118.During Manual D duct sizing, a technician selects a friction rate of 0.10 in. wc per 100 ft. Per the duct sizing table for this friction rate, a 6-inch round duct carries approximately 100 CFM and an 8-inch round duct carries approximately 200 CFM. A branch run must deliver 180 CFM to a bedroom register. Which duct size should the technician select?Planning and Layout
  19. 119.What is the primary function of the condenser coil in a residential split-system air-conditioning system?Cooling and Refrigeration
  20. 120.A technician performs a pressure pan test as part of duct leakage diagnostics. With a blower door depressurizing the house to -25 Pa relative to outdoors, the technician seals a pan over a supply register and reads 0.3 Pa on the manometer. What does this low reading most likely indicate?Ventilation and Air Distribution
  21. 121.A split-phase induction motor fails to reach running speed and hums loudly without starting. A technician suspects the centrifugal switch. What is the normal function of this switch during motor operation?Controls, Electrical and Safety
  22. 122.A 90% AFUE non-condensing furnace uses an induced-draft fan to create a slight positive pressure in the vent while flue gas temperatures remain above the dew point, avoiding condensation. This describes which venting category?Heating Systems
  23. 123.A rooftop package unit's compressor control circuit includes a high-pressure switch. What is the primary function of this safety device?Cooling and Refrigeration
  24. 124.A Manual J load calculation for a 3-bedroom home uses the standard default occupancy formula of (bedrooms + 1) to estimate the number of occupants for internal heat gain purposes. Using a typical Manual J allowance of 230 Btu/hr sensible heat gain per person, what is the total occupant sensible heat gain added to the cooling load?Planning and Layout
  25. 125.What is the primary purpose of a suction line accumulator installed near the compressor inlet on some air-conditioning and heat pump systems?Cooling and Refrigeration
  26. 126.A gas furnace is rated at 100,000 Btu/hr input at sea level. It will be installed at an elevation of 6,000 feet. Applying the standard derating guideline of 4% reduction in input capacity per 1,000 feet of elevation above 2,000 feet, what is the furnace's derated input capacity at this altitude?Planning and Layout
  27. 127.On a heat pump thermostat wiring system, the reversing valve solenoid is wired to the O terminal (energized in cooling mode) on most manufacturers' equipment. If a technician mistakenly wires the reversing valve to the B terminal instead, what will happen when the system calls for cooling?Controls, Electrical and Safety
  28. 128.A technician replaces a MERV 8 filter with a MERV 13 filter of the same physical dimensions, without modifying the blower or ductwork. What is the most likely operational result?Ventilation and Air Distribution
  29. 129.A technician is running 24-volt thermostat wire for a distance of 200 feet to a furnace. Using a standard wire-gauge distance chart (18 AWG rated for runs up to 100 ft, 16 AWG for 100–200 ft, 14 AWG for 200–300 ft) to keep voltage drop under 5%, which wire gauge should be installed for this run?Controls, Electrical and Safety
  30. 130.A Category I natural-draft furnace vents into a single-wall metal vent connector routed through an unconditioned attic space near wood framing. Per code, what minimum clearance to combustible materials must this single-wall vent connector maintain?Heating Systems
  31. 131.A room has a calculated sensible heat gain of 24,000 BTU/hr. The design temperature split (supply air to room air) is 20°F. Using the standard sensible heat formula, how much supply airflow (CFM) is required to offset this load?Ventilation and Air Distribution
  32. 132.A contractor explains to a customer why a new unit's SEER2 rating is numerically lower than a comparable older unit's SEER rating, even though cooling performance is similar. What is the primary reason for this difference?Cooling and Refrigeration
  33. 133.A supply trunk duct leaves the plenum carrying 1,600 CFM. The first branch takeoff delivers 400 CFM to a bedroom register. According to Manual D trunk duct design principles, what CFM must the remaining downstream trunk duct be sized to carry?Planning and Layout
  34. 134.A technician recovers used refrigerant from a repair job and wants to sell it to another company for reuse in a different owner's system. Per EPA regulations, this refrigerant must first be processed by a certified reclaimer to meet the purity standards defined in:Cooling and Refrigeration
  35. 135.A technician inspects a system and finds the suction line heavily frosted all the way back to the compressor, with a measured superheat of 0°F. What immediate risk does this condition pose to the compressor?Cooling and Refrigeration
  36. 136.A technician has locked and tagged out the disconnect for a rooftop condensing unit before servicing it. According to Cal/OSHA lockout/tagout procedures, what must be done immediately after applying the lock and tag but before beginning work?Controls, Electrical and Safety
  37. 137.A 100,000 BTU/hr gas furnace is installed in a confined space that obtains all combustion air from outdoors through two permanent openings, one near the top and one near the bottom of the enclosure. Per CMC combustion air sizing rules (1 sq in per 4,000 BTU/hr for outdoor air openings), what is the minimum required free area for EACH opening?Ventilation and Air Distribution
  38. 138.A technician completes a repair on a leaking residential split system. Under EPA Section 608 regulations, what must be done with the refrigerant remaining in the system before it is opened to the atmosphere for the repair?Cooling and Refrigeration
  39. 139.A load calculation determines a home's total cooling requirement to be 42,000 Btu/hr. How many tons of cooling capacity should the equipment be sized for?Planning and Layout
  40. 140.A technician mistakenly connects R-22 service gauges rated for a maximum working pressure of 350 psig to an R-410A system sitting in direct sun, where the liquid line temperature reads 130°F. If R-410A's saturation pressure at 130°F is approximately 401 psig, what is the primary safety concern?Cooling and Refrigeration
  41. 141.Per the California Mechanical Code, which of the following materials is NOT approved as a primary sealant for joints and seams in metal ductwork?Ventilation and Air Distribution
  42. 142.A technician measures return air entering the evaporator coil at 75°F and supply air leaving the coil at 55°F on a properly operating split system. What does this 20°F temperature split indicate?Cooling and Refrigeration
  43. 143.During a combustion safety inspection, a technician suspects a cracked heat exchanger in a gas furnace. Which diagnostic method provides the most reliable confirmation of this hazard?Controls, Electrical and Safety
  44. 144.A technician is teaching an apprentice the basic refrigeration cycle. Which of the following correctly lists the refrigerant flow sequence starting from the compressor?Cooling and Refrigeration
  45. 145.A single-story home in a California climate zone has identical-sized windows on both the east and west exterior walls. When performing a Manual J cooling load calculation, which orientation typically contributes the greatest solar heat gain load during peak afternoon design conditions?Planning and Layout
  46. 146.A technician is adjusting manifold gas pressure on a new natural gas furnace with a single-stage gas valve. What is the typical factory-specified manifold pressure for natural gas at sea level?Heating Systems
  47. 147.A technician is calibrating a mechanical thermostat with an adjustable heat anticipator. The furnace's primary gas valve control circuit draws 0.4 amp. Where should the heat anticipator pointer be set?Controls, Electrical and Safety
  48. 148.A furnace supplies 1,200 CFM to a rectangular supply plenum. To keep air velocity within the recommended maximum of 700 feet per minute, what is the minimum required cross-sectional area of the plenum?Planning and Layout
  49. 149.A technician measures static pressure immediately before and after the evaporator coil: +0.25 in. w.c. entering and -0.35 in. w.c. leaving. The manufacturer specifies a maximum coil pressure drop of 0.30 in. w.c. at rated airflow. What is the measured pressure drop across the coil, and what does it indicate?Ventilation and Air Distribution
  50. 150.A technician installs a TXV on an evaporator coil with a long refrigerant distributor and multiple circuits, resulting in significant pressure drop across the coil. Why should an externally equalized TXV be used instead of an internally equalized valve in this application?Cooling and Refrigeration