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CSLB C-20 HVAC Contractor practice questions

200 free questions with answers and explanations.

Practice test
  1. 51.A technician is designing ductwork serving a conference room with a target noise criterion of NC-30. The current design routes air through a small branch duct with a discharge velocity of about 900 fpm at the diffuser. Which design change would most effectively help achieve the noise target?Ventilation and Air Distribution
  2. 52.Per the California Mechanical Code and referenced NFPA 96 provisions, what is the minimum required clearance from an unenclosed, unlisted commercial kitchen grease exhaust duct to combustible construction?Ventilation and Air Distribution
  3. 53.A technician installs a residential air conditioner that is one full size larger than the Manual J calculated load requires, believing it will cool the home faster. What is the most likely negative result of this oversizing?Planning and Layout
  4. 54.A commercial rooftop unit supplies a constant 4,000 CFM to a zone. Per ASHRAE 62.1, the required outdoor air ventilation rate for the space is calculated at 800 CFM. What minimum outdoor air damper position, expressed as a percentage of total supply airflow, should the technician set to meet this requirement?Ventilation and Air Distribution
  5. 55.A technician suspects a restricted liquid line filter drier on an operating system. Which field test would best confirm this diagnosis?Cooling and Refrigeration
  6. 56.A technician uses a megohmmeter to test the insulation resistance of a compressor motor winding to ground and reads 0.3 megohms. According to common industry standards, what does this reading indicate?Controls, Electrical and Safety
  7. 57.On a mechanical blueprint, a branch duct takeoff is labeled with the symbol 'VD.' What does this symbol most likely indicate?Planning and Layout
  8. 58.A technician observes that a TXV-equipped system's suction pressure and superheat readings oscillate repeatedly, cycling between high and low values every few seconds instead of stabilizing. This behavior, known as valve 'hunting,' is most commonly caused by:Cooling and Refrigeration
  9. 59.A commercial rooftop package HVAC unit has a 125-volt, 20-amp service receptacle installed for technician use during maintenance. Per California Electrical Code requirements, what protection must this receptacle have?Controls, Electrical and Safety
  10. 60.A technician wants to pressure test a repaired refrigeration system for leaks using a compressed gas. Which gas is strictly prohibited for this purpose because it can react explosively with refrigerant oil residue under pressure?Cooling and Refrigeration
  11. 61.A heat pump delivers 22,000 Btu/h of heating output while drawing 2,800 watts of electrical input. What is the approximate COP (coefficient of performance) of this unit?Heating Systems
  12. 62.A technician is explaining filtration to a homeowner. What does a higher MERV rating primarily indicate about an air filter?Ventilation and Air Distribution
  13. 63.Per common industry convention for refrigerant cylinder color coding (AHRI guideline colors), what color is a virgin R-410A refrigerant cylinder typically painted?Cooling and Refrigeration
  14. 64.A heat recovery ventilator (HRV) has a rated sensible recovery effectiveness (SRE) of 70%. On a winter day, outdoor air is 20°F and indoor exhaust air is 70°F. Approximately what temperature will the incoming ventilation air reach after passing through the HRV core, before any additional heating by the furnace?Ventilation and Air Distribution
  15. 65.A natural draft water heater is installed in a utility closet using the alternate single-opening combustion air method per the California Mechanical Code. The single opening is located within 12 inches of the ceiling and communicates with a space having adequate infiltration. What is the minimum required free area for this opening, expressed per BTU/hr of appliance input?Ventilation and Air Distribution
  16. 66.A duct system is routed entirely through an unconditioned attic, resulting in an estimated 15% loss of delivered cooling capacity due to duct heat gain. If the conditioned space requires 36,000 Btu/hr of delivered cooling, what equipment output capacity should be selected to compensate for this duct loss?Planning and Layout
  17. 67.A rooftop condensing unit operates in cold outdoor conditions (around 40°F), causing low head pressure and inadequate liquid pressure to feed the TXV properly. Which device is commonly used to maintain adequate head pressure under low-ambient conditions?Cooling and Refrigeration
  18. 68.A home has a 400 CFM range hood, a 200 CFM clothes dryer, and two 50 CFM bathroom exhaust fans all operating simultaneously, totaling 700 CFM of exhaust. The home's envelope and passive makeup air pathways can only supply 500 CFM of replacement air. Which hazardous condition is MOST likely to result?Ventilation and Air Distribution
  19. 69.A Manual J load calculation for a home in a California climate zone uses the 1% cooling design temperature rather than the historical all-time record high temperature. What is the primary reason for using this value instead of the record high?Planning and Layout
  20. 70.A newly installed duct system has a total supply and return airflow of 1,200 CFM. Duct leakage testing (CFM25) measures 65 CFM of total leakage. Title 24 requires new duct systems to have total leakage no greater than 6% of total system airflow. Does this system meet the leakage requirement?Planning and Layout
  21. 71.A Manual J calculation shows a total cooling load of 36,000 Btu/hr with a sensible heat ratio (SHR) of 0.75. If the design supply-to-return air temperature difference (ΔT) is 18°F, what CFM is required to satisfy the sensible portion of the load?Planning and Layout
  22. 72.A technician installs flexible supply duct in a joist bay but does not fully extend it, leaving it compressed to about 85% of its rated stretched length. What is the most significant effect on system performance?Planning and Layout
  23. 73.A technician needs to replace a failed compressor on a system with a liquid line service valve, without releasing refrigerant into the atmosphere. Which procedure allows the technician to isolate the system's refrigerant charge in the outdoor unit before opening the system?Cooling and Refrigeration
  24. 74.A newly renovated home has elevated indoor formaldehyde levels from off-gassing new cabinetry and flooring. Which strategy would most effectively reduce this indoor air quality concern?Ventilation and Air Distribution
  25. 75.A technician is adding oil to an R-410A residential compressor after a repair. Which type of oil must be used, and why?Cooling and Refrigeration
  26. 76.A client asks about R-32 refrigerant, which is classified as A2L under ASHRAE Standard 34. What does this classification indicate about the refrigerant?Cooling and Refrigeration
  27. 77.A technician is sizing a return air grille for a residential system to avoid customer noise complaints. Per common industry guidance (ACCA Manual D), what is the generally recommended maximum face velocity through a return air grille?Ventilation and Air Distribution
  28. 78.A technician measures a system's TESP at 0.95 in. w.c., but the air handler's rated maximum ESP is 0.50 in. w.c. Airflow is noticeably reduced. Which troubleshooting step should be performed FIRST?Ventilation and Air Distribution
  29. 79.A home has a conditioned volume of 12,000 cubic feet. A Manual J infiltration estimate uses a natural air change rate of 0.35 ACH. What is the estimated infiltration airflow in CFM?Planning and Layout
  30. 80.A Manual J calculation shows a design cooling load of 34,000 Btu/hr sensible and 6,000 Btu/hr latent (40,000 Btu/hr total). Per Manual S equipment selection guidelines, which criterion should the contractor prioritize when comparing available air conditioner models?Planning and Layout
  31. 81.A bathroom in new residential construction has no operable window. According to California Mechanical Code ventilation requirements, what minimum mechanical exhaust rate satisfies code if the fan runs continuously?Ventilation and Air Distribution
  32. 82.A technician is selecting a supply diffuser for a large open room and needs the air to travel across the space without creating a noticeable draft in the occupied zone. Which factor has the greatest direct effect on how far the diffuser will throw air?Ventilation and Air Distribution
  33. 83.A heat pump in heating mode has its outdoor coil covered in frost. The system automatically reverses to cooling mode briefly while the indoor blower continues running warm air. What component initiates this defrost cycle?Heating Systems
  34. 84.A single compressor-motor unit has a nameplate rated-load current (RLA) of 18 amps. Per NEC 440.12, what is the minimum ampacity rating required for the disconnecting means serving this compressor (based on the 115% rule), rounded up to the nearest standard disconnect size?Controls, Electrical and Safety
  35. 85.A zoned residential system uses motorized zone dampers with a barometric bypass duct to relieve excess static pressure when only the smallest zone is calling. A technician notices that with only that small zone active, the supply air feels unusually cold and there is noticeable turbulent airflow noise near the bypass duct connection. What is the most likely explanation?Ventilation and Air Distribution
  36. 86.A furnace blower has a rated total external static pressure (ESP) capability of 0.50 in. w.c. The installed evaporator coil has a pressure drop of 0.20 in. w.c., and the filter has a pressure drop of 0.08 in. w.c. How much static pressure is available for the supply and return ductwork?Planning and Layout
  37. 87.A residential compressor repeatedly shuts off on a safety control and immediately restarts within seconds, causing high inrush current each time. What component should a technician install to prevent this damaging short-cycling?Cooling and Refrigeration
  38. 88.A technician is reading a mechanical blueprint drawn at a scale of 1/4 inch = 1 foot. A duct run measures 2 inches on the drawing. What is the actual length of the duct run in the field?Planning and Layout
  39. 89.A thermostat with a wide temperature differential is causing a furnace to short cycle excessively. What adjustment would most directly correct this issue on a mechanical thermostat?Controls, Electrical and Safety
  40. 90.A technician measures compressor discharge line temperature at 260°F on an R-410A scroll compressor system where the condensing temperature (from head pressure) corresponds to 125°F saturation. What does this reading most likely indicate?Cooling and Refrigeration
  41. 91.A duct system has a total effective length of 150 feet. The air handler has 0.50 in. w.c. total available static pressure, and fittings/coil/filter losses consume 0.35 in. w.c. What friction rate (in. w.c. per 100 ft) should be used to size the duct system?Ventilation and Air Distribution
  42. 92.Per the California Mechanical Code, what is the default maximum length of a clothes dryer exhaust duct (measured with two 90-degree elbows), unless a different length is otherwise permitted by the dryer manufacturer's installation instructions or an engineered calculation?Ventilation and Air Distribution
  43. 93.A homeowner complains of headaches and dizziness that improve when they leave the house. A technician suspects low-level carbon monoxide exposure from a furnace. What is the most likely underlying cause the technician should investigate first?Controls, Electrical and Safety
  44. 94.Per ASHRAE 62.2 whole-house mechanical ventilation requirements, a home has 1,800 square feet of conditioned floor area and 3 bedrooms. What is the minimum required continuous whole-house ventilation rate?Ventilation and Air Distribution
  45. 95.A gas furnace has an input rating of 80,000 Btu/hr and an AFUE rating of 92%. A Manual J calculation shows the home's design heating load is 68,000 Btu/hr. What is the furnace's actual heating output capacity, and is it adequately sized for the load?Planning and Layout
  46. 96.A technician is replacing a failed compressor in a residential split system and notes the original compressor is a scroll type. What operational characteristic distinguishes a scroll compressor from a reciprocating compressor?Cooling and Refrigeration
  47. 97.On a mechanical blueprint, a duct symbol shown penetrating a rated wall assembly includes a hatched rectangular symbol labeled 'FD'. What does this symbol indicate to the installing technician?Planning and Layout
  48. 98.Per California's Title 24 Energy Code, what is the minimum insulation R-value generally required for new supply ducts installed in an unconditioned attic space in most California climate zones?Ventilation and Air Distribution
  49. 99.During a service call, a technician measures the liquid line temperature leaving the condenser at 95°F. The high-pressure gauge corresponds to a saturation temperature of 105°F. What is the subcooling value?Cooling and Refrigeration
  50. 100.A technician measures suction line temperature at 55°F on a fixed-orifice system. The suction pressure gauge reads a saturation temperature of 40°F. What is the superheat, and what does it generally indicate about the charge if the target superheat is 10°F?Cooling and Refrigeration