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CSLB C-20 HVAC Contractor practice questions

200 free questions with answers and explanations.

Practice test
  1. 151.A single-phase compressor motor has a rated-load current (RLA) of 20 amps and a locked-rotor amperage (LRA) of 110 amps. Per NEC Section 440.22(A), the maximum branch-circuit short-circuit and ground-fault protective device is generally limited to 175% of the motor's RLA. What is the maximum standard breaker size permitted for this circuit?Controls, Electrical and Safety
  2. 152.A technician wires a new three-phase condenser fan motor and, upon startup, observes the fan blade spinning in the wrong direction, reducing airflow across the coil. What is the correct corrective action?Controls, Electrical and Safety
  3. 153.Per Cal/OSHA regulations, what is the permissible exposure limit (PEL) for carbon monoxide as an 8-hour time-weighted average?Controls, Electrical and Safety
  4. 154.A zoned duct system has a total design airflow of 1,600 CFM. When only the smallest zone is calling for cooling, its zone damper allows only 600 CFM to the occupied space. To protect the blower and prevent excessive static pressure, a bypass duct routes excess air back to the return plenum. What CFM must the bypass duct be sized to handle under this condition?Planning and Layout
  5. 155.A client's split system uses a thermostatic expansion valve (TXV) instead of a fixed orifice. What is the primary advantage of the TXV over a fixed-orifice metering device?Cooling and Refrigeration
  6. 156.After repairing a refrigerant leak on a residential split system, a technician evacuates the system using a vacuum pump and a micron gauge before charging. To adequately remove moisture and non-condensable gases, the system should be evacuated to approximately:Cooling and Refrigeration
  7. 157.A technician finds that a 24V control transformer's internal fuse keeps blowing immediately after replacement. Voltage checks show 24V present at the transformer secondary before connecting the thermostat wires. What is the most likely cause?Controls, Electrical and Safety
  8. 158.What is the primary function of the evaporator coil in a residential split-system air conditioner?Cooling and Refrigeration
  9. 159.A technician performs a combustion appliance zone (CAZ) worst-case depressurization test with all exhaust fans and the air handler running. The CAZ depressurizes to -5 Pa relative to outdoors, while the manufacturer's spillage-safe limit for the atmospherically vented water heater is -3 Pa. What should the technician do?Ventilation and Air Distribution
  10. 160.A technician recovers refrigerant from a customer's failed system and wants to sell it to a third party. Per EPA regulations, what must happen to this refrigerant before it can be resold to a different owner?Cooling and Refrigeration
  11. 161.A technician performs an annual leak check on a commercial comfort cooling chiller with a 75 lb refrigerant charge and calculates an 18% annual leak rate. Under EPA Section 608 refrigerant management requirements, what must occur?Cooling and Refrigeration
  12. 162.During Manual D duct design, a system has a total effective length (TEL) of 150 feet and an available static pressure of 0.08 in. w.c. What friction rate (in inches of water column per 100 feet) should be used to size the ductwork?Planning and Layout
  13. 163.A client is installing a kitchen range hood rated at 500 CFM. Per the California Mechanical Code, what additional requirement is triggered by exceeding the 400 CFM threshold?Ventilation and Air Distribution
  14. 164.A contractor explains to a client that new equipment ratings use SEER2 instead of the older SEER metric. What is the primary reason the testing standard changed from SEER to SEER2?Cooling and Refrigeration
  15. 165.For new residential construction in California, Title 24 duct leakage test results must be verified and documented by whom, and on which compliance form?Ventilation and Air Distribution
  16. 166.A Manual J heat loss calculation includes an exterior wall segment with a net area of 250 square feet and an assembly U-factor of 0.32 Btu/hr·ft²·°F. The design temperature difference (indoor design temp minus the 99% heating design temp) is 45°F. What is the wall's heat loss contribution to the total heating load?Planning and Layout
  17. 167.A homeowner installs a carbon monoxide detector in a hallway near bedrooms. Per general safety guidelines, where should CO detectors be mounted for proper sensing?Controls, Electrical and Safety
  18. 168.A heat pump system has a balance point of 30°F. On a day when outdoor temperature drops to 20°F, what happens to meet the building's heating load?Heating Systems
  19. 169.During a load calculation, a technician must size two permanent combustion air openings using horizontal ducts connecting a mechanical closet directly to outdoors. The closet houses a furnace and water heater with a combined input of 240,000 Btu/h. Per the California Mechanical Code, what is the minimum free area required for EACH opening?Heating Systems
  20. 170.A technician performs duct leakage diagnostics and finds that of the system's total 300 CFM of duct leakage, roughly 220 CFM occurs on the return side, with the return duct routed through a 140°F attic. What is the most likely operational consequence during cooling season?Ventilation and Air Distribution
  21. 171.A technician charges a residential split system on an 85°F day but notices head pressure is significantly higher than the pressure-temperature chart predicts for that ambient temperature, even after verifying correct charge weight. What is the most likely cause?Cooling and Refrigeration
  22. 172.A furnace blower has 0.50 in. wc of total external static pressure (ESP) available. Manufacturer data shows the cooling coil consumes 0.20 in. wc and the air filter consumes 0.08 in. wc of that available pressure. How much static pressure remains available for duct friction losses in the supply and return ductwork combined?Planning and Layout
  23. 173.Before removing a run capacitor from a de-energized air conditioning condensing unit, a technician should first do which of the following to prevent injury?Controls, Electrical and Safety
  24. 174.A technician responds to a call where a compressor hums but fails to start. The nameplate lists RLA (rated load amps) of 18A and LRA (locked rotor amps) of 95A. A clamp meter shows the compressor continuously drawing 94A with no increase in speed before the overload trips. This reading most likely indicates:Cooling and Refrigeration
  25. 175.A contractor is preparing to size a new residential HVAC system. What is the primary purpose of performing a Manual J calculation before selecting equipment?Planning and Layout
  26. 176.Which venting category describes a furnace that operates with a negative vent pressure and produces non-condensing flue gases, typical of an older standard-efficiency atmospheric furnace?Heating Systems
  27. 177.A technician observes continuous bubbles moving through the liquid line sight glass of an operating R-410A split system. What does this most likely indicate?Cooling and Refrigeration
  28. 178.A 90% AFUE Category I natural-draft furnace is replaced with new equipment in the same location. A technician notes the old vent connector had a barometric draft damper installed in the vent pipe. What is the primary function of this component?Heating Systems
  29. 179.A technician is sizing a gas supply pipe for a furnace with an input rating of 120,000 Btu/h using natural gas with a heating value of 1,000 Btu per cubic foot. What cubic feet per hour (cfh) demand value should be used when consulting the gas pipe sizing table?Heating Systems
  30. 180.A new 95% AFUE furnace uses an electronic ignition system with no standing pilot. A technician notices a small ceramic rod glowing orange near the burners at the start of the heating cycle before gas flow begins. What ignition component is this?Heating Systems
  31. 181.A homeowner installs a new 96% AFUE condensing furnace. During inspection, a technician checks the condensate drain system. Which component is required to prevent flue gases from escaping through the condensate drain line?Heating Systems
  32. 182.A furnace rated at 80,000 Btu/h input is being installed at an elevation of 6,500 feet. Per manufacturer instructions following standard altitude derate practice, input must be reduced by 4% for each 1,000 feet of elevation above 2,000 feet. What is the derated input rating the technician should use when sizing the orifice?Heating Systems
  33. 183.A commercial hydronic boiler system experiences a sudden loss of water due to a leaking pipe fitting. Which safety device is designed to shut down the burner before the boiler operates with insufficient water level?Heating Systems
  34. 184.A technician is troubleshooting a furnace that ignites briefly then shuts off after a few seconds, displaying a flame sensing fault code. Testing the flame sensor with a microammeter during burner operation shows only 0.5 microamps DC, below the minimum required. What does this most likely indicate?Heating Systems
  35. 185.In a hydronic heating system, a technician is deciding where to install the circulator pump relative to the expansion tank connection point (the point of no pressure change). For proper system operation, where should the pump be installed?Heating Systems
  36. 186.A technician installs a two-stage gas furnace. On a moderately cold day, the thermostat calls for heat and the furnace initially fires at low stage (65% of full input). After several minutes, the space temperature continues to drop and the thermostat sends a second-stage call. What is the primary benefit of this staged operation?Heating Systems
  37. 187.A furnace has an input rating of 100,000 Btu/h and is rated at 80% AFUE. The blower delivers 1,200 CFM across the heat exchanger. Using the standard formula Btu/h = 1.08 × CFM × ΔT, what is the approximate temperature rise across the heat exchanger?Heating Systems
  38. 188.A technician is installing a new 92% AFUE condensing furnace. The furnace manufacturer's instructions specify using Schedule 40 PVC for the vent piping. According to California Mechanical Code (CMC) and common practice, what is the maximum recommended unsupported horizontal length for this type of vent pipe between hangers?Heating Systems
  39. 189.A client's new construction home features a radiant floor heating system in the main living areas. Which of the following components is essential for protecting the radiant floor tubing from excessively hot water temperatures from the boiler?Heating Systems
  40. 190.A technician is installing a new gas furnace in a utility room that is considered a 'confined space' according to the Uniform Mechanical Code (UMC). The total input rating of all gas appliances in this space is 150,000 Btu/h. No outdoor combustion air ducts are planned. What is the minimum required free area for a single opening connecting directly to an adjacent unconfined space?Heating Systems
  41. 191.A homeowner reports that their gas furnace cycles on and off rapidly, never completing a full heating cycle. The technician observes that the main burner lights, but then extinguishes after a short period, and the blower never fully engages. What is the most likely cause of this short cycling?Heating Systems
  42. 192.A hydronic heating system is being installed in a commercial building. To ensure proper heat delivery and prevent air-related issues, the air separator should be installed at which location in the system?Heating Systems
  43. 193.A technician is evaluating an existing gas furnace in an unconditioned attic space. The furnace has a natural draft vent system, and the vent connector needs replacement. Per Uniform Mechanical Code (UMC) standards, what is the minimum required rise for the vent connector from the furnace flue collar to the vent pipe or chimney connection point?Heating Systems
  44. 194.A heat pump system is experiencing frequent trips of the circuit breaker for the outdoor unit. The technician finds that the compressor draws excessively high amperage during startup attempts. Which of the following is the most likely cause?Heating Systems
  45. 195.A hydronic heating system uses a boiler to heat water, which is then circulated through baseboard radiators. What type of pump is typically used to move the heated water through the closed loop system?Heating Systems
  46. 196.A two-stage gas furnace is installed in a home. The homeowner reports that the furnace runs continuously for long periods during moderate weather, but never seems to reach its 'full power' setting. What is the most likely reason for this behavior?Heating Systems
  47. 197.A technician is performing a heat loss calculation for a home to properly size a replacement furnace. The calculation determines the home loses 60,000 Btu/h at the design outdoor temperature. The new furnace has an Annual Fuel Utilization Efficiency (AFUE) of 90%. What is the minimum required input rating for the new furnace to meet the heat loss?Heating Systems
  48. 198.A technician is performing a combustion analysis on a natural gas furnace. The measured CO (carbon monoxide) level in the flue gas is 400 ppm (parts per million) undiluted. What action should the technician take, according to safety protocols and code requirements?Heating Systems
  49. 199.A residential heat pump system is operating in heating mode. The outdoor unit's fan motor is running, but the compressor is not engaging, and the system is blowing cool air indoors. After checking power, what is the next most probable component to troubleshoot?Heating Systems
  50. 200.A residential HVAC system design requires a total airflow of 1,200 CFM. The system is designed with a constant volume fan. If the static pressure in the supply plenum increases due to a partially closed damper, what is the most likely immediate effect on the system's airflow?Planning and Layout