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CSLB C-20 HVAC Contractor practice questions

200 free questions with answers and explanations.

Practice test
  1. 1.During a combustion safety inspection, a technician uses a draft gauge at the draft hood of a natural-draft gas furnace and measures a positive pressure reading instead of the expected negative draft. What does this most likely indicate?Controls, Electrical and Safety
  2. 2.A branch duct supplies air to a bedroom register in an occupied living space. To avoid objectionable air noise, Manual D recommends the branch duct velocity not exceed approximately which of the following?Planning and Layout
  3. 3.A gas furnace's blower fails to start, causing the heat exchanger to overheat. Which safety control is designed to shut off the burners in this situation?Heating Systems
  4. 4.A blower motor is rated 1/2 HP with a full-load amperage (FLA) of 5.0 amps and a service factor (SF) of 1.15. What is the maximum current this motor can safely draw on a continuous basis?Controls, Electrical and Safety
  5. 5.A technician installs a return filter grille with a net free filter opening of 16 inches by 20 inches to handle 1,000 CFM of return air. What is the approximate filter face velocity, and does it fall within the commonly recommended maximum of about 300 fpm for extended filter life and low pressure drop?Ventilation and Air Distribution
  6. 6.A vented under-floor crawlspace measures 1,800 square feet and does not have a Class I vapor retarder installed over the ground. Using the standard 1/150 ratio, what minimum total net free ventilation area is required for this crawlspace?Ventilation and Air Distribution
  7. 7.A residential air handler supplies 1,200 CFM. To avoid excessive noise and static pressure, a sheet-metal return trunk duct should be sized so that air velocity does not exceed 500 FPM. What minimum cross-sectional area should the return trunk duct have?Ventilation and Air Distribution
  8. 8.A technician is commissioning a new 3-ton residential split-system air conditioner. Using the standard industry rule of thumb for cooling airflow, what target airflow should the system deliver?Ventilation and Air Distribution
  9. 9.A technician is dispatched to inspect an underground equipment vault housing a large commercial air handler before performing maintenance. Per Cal/OSHA confined space regulations, what must be done before entry?Controls, Electrical and Safety
  10. 10.A hydronic baseboard heating system has multiple zones, each controlled independently. What component allows one zone's thermostat to call for heat without activating water flow to the other zones?Heating Systems
  11. 11.A commercial refrigeration system uses a pump-down cycle to prevent liquid refrigerant migration into the compressor during the off cycle. Where is the liquid line solenoid valve typically installed, and what causes it to close?Cooling and Refrigeration
  12. 12.A technician must service a package HVAC unit located on a low-slope commercial roof, working within 6 feet of the unguarded roof edge. Per Cal/OSHA fall protection requirements for low-slope roofs, at what minimum height above the lower level must fall protection (such as a guardrail, warning line system, or personal fall arrest) generally be provided?Controls, Electrical and Safety
  13. 13.A furnace requires 100,000 Btu/hr gas input, and the gas piping run from the meter to the appliance is 40 feet including fittings. Using a simplified gas pipe sizing table, a 1/2-inch pipe at 40 feet carries 56,000 Btu/hr, a 3/4-inch pipe carries 117,000 Btu/hr, and a 1-inch pipe carries 220,000 Btu/hr. What is the minimum pipe size the technician must install?Planning and Layout
  14. 14.Per California Title 24 requirements for a newly installed residential duct system, what is the maximum allowable total duct leakage as verified by a HERS rater's diagnostic test?Ventilation and Air Distribution
  15. 15.A 24-volt, 40 VA control transformer powers a thermostat and relay circuit. What is the maximum continuous current this transformer can safely supply?Controls, Electrical and Safety
  16. 16.A Manual J cooling load calculation for a west-facing window uses a peak solar heat gain factor of 200 Btu/hr per square foot at design conditions. The window has a net area of 40 square feet and a solar heat gain coefficient (SHGC) of 0.30. What is the estimated peak solar heat gain through this window?Planning and Layout
  17. 17.A technician is charging a new TXV split system by weight per the manufacturer's charging chart, then fine-tunes using subcooling. After charging, measured subcooling is 4°F, but the manufacturer specifies a target of 12°F. What should the technician do?Cooling and Refrigeration
  18. 18.A technician measures a run capacitor rated 35 µF (±6% tolerance) and gets a reading of 28 µF on a capacitance meter. What should the technician conclude?Controls, Electrical and Safety
  19. 19.A commercial office space measuring 2,000 sq ft has a design occupancy of 20 people. Using the ASHRAE 62.1 Ventilation Rate Procedure default rates of 5 CFM per person plus 0.06 CFM per square foot for office space, what is the minimum required outdoor air ventilation rate?Ventilation and Air Distribution
  20. 20.A Manual D duct design specifies a total system airflow of 1,200 CFM distributed among five supply branches. Four branches are measured after installation and deliver 220, 180, 260, and 240 CFM respectively. Assuming no duct leakage, what CFM must the fifth branch deliver to match the design total?Planning and Layout
  21. 21.Per the Uniform Mechanical Code, a furnace installed in a small utility closet with a volume of 40 cubic feet and no direct free communication with additional adjoining rooms is classified as being in which type of space?Heating Systems
  22. 22.A mechanical blueprint includes an equipment schedule table listing unit tag 'FAU-1' with a specified airflow of 1,600 CFM and a rated output of 80,000 Btu/hr. Before beginning rough-in, where should a technician look on the plans to confirm this equipment information?Planning and Layout
  23. 23.On a residential split system equipped with a thermostatic expansion valve (TXV), where is the filter drier normally installed?Cooling and Refrigeration
  24. 24.A technician replacing a failed dual run capacitor rated 45 µF for the compressor has only two single 25 µF capacitors in stock. If wired in parallel to substitute for the original capacitor, what is the resulting capacitance, and is it acceptable?Controls, Electrical and Safety
  25. 25.What is the primary purpose of a start capacitor in a single-phase motor circuit, and when is it typically removed from the circuit?Controls, Electrical and Safety
  26. 26.Per California Title 24/CALGreen requirements, a bathroom exhaust fan intended for continuous whole-house ventilation operation must have a maximum sound rating, when tested at 0.25 in. w.c., of no more than how many sones?Ventilation and Air Distribution
  27. 27.A rectangular supply duct measures 8 inches by 14 inches and carries 800 CFM. What is the approximate air velocity inside the duct?Ventilation and Air Distribution
  28. 28.A technician performs a Title 24 duct leakage test using a duct blaster. Before pressurizing the duct system to 25 Pascals, the technician seals all supply and return registers with tape. What does this test procedure measure?Ventilation and Air Distribution
  29. 29.A Manual T register selection process determines a supply diffuser has a rated throw of 12 feet at a terminal velocity of 50 fpm. The diffuser is installed in a room where the opposite wall is 18 feet away. What is the most likely consequence of this selection?Planning and Layout
  30. 30.A duct system operating at 1,200 CFM produces 0.60 in. w.c. of total external static pressure. If airflow is increased to 1,400 CFM through the same unchanged duct system, what is the new approximate static pressure (fan affinity law: pressure varies with the square of the CFM ratio)?Ventilation and Air Distribution
  31. 31.In a heat pump system, what component allows the unit to switch between heating and cooling modes by redirecting refrigerant flow?Heating Systems
  32. 32.A homeowner asks what type of EPA Section 608 certification is required to service a small window air conditioner containing less than 5 pounds of refrigerant that will be repaired without removing the sealed system.Cooling and Refrigeration
  33. 33.A Manual D duct design must deliver a total system airflow of 1,500 CFM to match the equipment's rated output. A specific bedroom has a calculated heat load of 3,000 Btu/hr out of a whole-house total load of 45,000 Btu/hr. Using the proportional load-based method for branch duct airflow allocation, how much airflow should be routed to this bedroom's branch duct?Planning and Layout
  34. 34.A technician is charging a system using R-407C, a zeotropic refrigerant blend. Why must this refrigerant be added to the system as a liquid rather than a vapor?Cooling and Refrigeration
  35. 35.A technician is using a manufacturer's target superheat chart to charge a fixed-orifice metering device system. Which two measurements are required to determine the correct target superheat value from the chart?Cooling and Refrigeration
  36. 36.A technician is recovering refrigerant from a residential system into a DOT-approved recovery cylinder. To prevent hydrostatic overpressure and cylinder rupture, filling should stop at approximately what percentage of the cylinder's rated weight capacity?Cooling and Refrigeration
  37. 37.A duct system must deliver a sensible cooling load of 24,000 Btu/hr with a supply air temperature drop (ΔT) of 20°F. Using the standard sensible heat formula, what CFM is required?Planning and Layout
  38. 38.A technician must perform diagnostic work on an energized 480-volt panel where de-energization is not feasible due to critical operations. Per Cal/OSHA electrical safety requirements, what must be used to protect the technician?Controls, Electrical and Safety
  39. 39.A new 96% AFUE condensing furnace is installed. Which venting material is code-approved for its Category IV flue gas venting?Heating Systems
  40. 40.A hydronic heating system develops persistent air bubbles in the baseboard radiators, causing gurgling noises and reduced heat output. Which component is designed to remove entrained air from the system?Heating Systems
  41. 41.A client's small window air conditioner has no adjustable expansion valve. A technician explains that the unit uses a capillary tube as its metering device. Which statement best describes this device?Cooling and Refrigeration
  42. 42.A return air grille measuring 20 inches by 20 inches has a manufacturer-rated free area of 75%. To keep the return air face velocity at or below the recommended maximum of 500 feet per minute for noise control, what is the maximum CFM this grille should handle?Planning and Layout
  43. 43.In a closed hydronic heating loop, what is the primary purpose of the expansion tank?Heating Systems
  44. 44.A technician is installing a TXV remote sensing bulb on a 1-1/8 inch OD horizontal suction line (a larger diameter line). Per standard industry practice, where should the bulb be mounted for accurate sensing?Cooling and Refrigeration
  45. 45.A compressor motor is rated with a full-load amperage (FLA) of 12 amps and has no internal thermal overload protection. Per standard electrical protection practice, what is the maximum overload device trip setting (at 125% of FLA)?Controls, Electrical and Safety
  46. 46.A technician finds that one bedroom on a residential system receives noticeably too much airflow while another bedroom receives too little, even though the total system CFM measured at the air handler is correct. What is the appropriate corrective action?Ventilation and Air Distribution
  47. 47.A residential split-system air conditioner is rated at 3 tons of cooling capacity. Using the standard rule-of-thumb airflow requirement commonly applied for typical comfort cooling systems, what design supply airflow should the duct system be sized to deliver?Planning and Layout
  48. 48.A homeowner's older standing-pilot gas furnace has a pilot flame that lights but the main burner never ignites, and the pilot eventually goes out. What component is the most likely cause?Heating Systems
  49. 49.A technician is replacing a failing PSC blower motor with an ECM (electronically commutated motor) blower on a variable-speed furnace. What is the main operational advantage of the ECM design compared to the PSC motor it replaces?Controls, Electrical and Safety
  50. 50.An apprentice is connecting a standard refrigeration manifold gauge set to a system for the first time. Which hose color should be connected to the high-pressure (liquid) service valve?Cooling and Refrigeration