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1. Which of the following is the primary refrigerant used in most new residential air conditioning systems after R-22 phaseout? A. R-12 B. R-134a C. R-410A D. R- 123 Answer: C. R-410A Explanation: R-410A replaced R-22 in most residential applications due to its zero ozone depletion potential and compliance with EPA regulations. 2. In Nevada, the C-21B license specifically covers work in: A. Refrigeration only B. Heating, cooling, and ventilation systems C. Plumbing installation D. Electrical panel installation Answer: B. Heating, cooling, and ventilation systems Explanation: The C-21B scope is limited to installing and servicing air conditioning, refrigeration, and ventilation systems, excluding unrelated trades like plumbing or main electrical service work. 3. The term SEER refers to: A. Seasonal Energy Efficiency Ratio B. Standard Electrical Equipment Rating C. Seasonal Electrical Efficiency Rate D. Standard Energy Evaluation Report Answer: A. Seasonal Energy Efficiency Ratio Explanation: SEER measures the cooling output during a typical cooling season divided by the total electric energy input.
4. What is the minimum SEER rating required for new central AC units in Nevada as of 2023? A. 10 B. 13 C. 14 D. 16 Answer: C. 14 Explanation: Federal regulations require at least 14 SEER for split - system central ACs in the Southwest region, which includes Nevada. 5. The correct tool to measure superheat is: A. Voltmeter B. Ammeter C. Thermometer and pressure gauge D. Multimeter with ohms setting Answer: C. Thermometer and pressure gauge Explanation: Superheat is calculated using the measured suction line temperature and corresponding saturation temperature from a pressure reading. 6. A low superheat reading typically indicates: A. Overcharged system B. Undercharged system C. Flooded evaporator D. Restriction in liquid line Answer: C. Flooded evaporator Explanation: Low superheat means liquid refrigerant is not being fully vaporized in the evaporator, often caused by overfeeding. 7. In an R-410A system, high head pressure can be caused by: A. Dirty condenser coils B. Low ambient temperature C. Low refrigerant charge D. Oversized evaporator
B. Maintain constant evaporator pressure C. Regulate refrigerant flow into the evaporator D. Control condenser fan speed Answer: C. Regulate refrigerant flow into the evaporator Explanation: The expansion valve meters refrigerant to match load requirements and maintain proper superheat.
12. Which duct material is NOT recommended for outdoor use in Nevada’s climate? A. Sheet metal B. Fiberglass duct board C. Flexible insulated duct D. PVC-coated sheet metal Answer: B. Fiberglass duct board Explanation: Fiberglass duct board is susceptible to moisture damage and degradation from UV exposure. 13. What is the typical temperature drop across an evaporator coil in a properly charged system? A. 2–5°F B. 10–15°F C. 18–22°F D. 30–35°F Answer: C. 18–22°F Explanation: A temperature difference of 18–22°F between return and supply air is typical for efficient operation. 14. In Nevada, the Building Code requires condensate drains to: A. Discharge onto walkways B. Be directly connected to sewer lines without trap C. Terminate to an approved location without causing nuisance D. Discharge into storm drains Answer: C. Terminate to an approved location without causing nuisance Explanation: Drains must prevent water damage or safety hazards.
15. A capacitor’s microfarad rating must be: A. Exactly the same as the original B. Within ±10% of the original rating C. Twice the original rating for better performance D. Irrelevant to motor function Answer: B. Within ±10% of the original rating Explanation: Too much deviation can cause motor overheating or reduced efficiency. 16. What is the common low-voltage control circuit voltage in HVAC systems? A. 12V B. 24V C. 48V D. 120V Answer: B. 24V Explanation: 24V AC is standard for thermostats and control relays. 17. When brazing copper refrigerant lines, nitrogen is used to: A. Increase flame temperature B. Prevent oxidation inside the tubing C. Speed up brazing process D. Reduce cost of brazing Answer: B. Prevent oxidation inside the tubing Explanation: Nitrogen flow prevents scale formation that can clog system components. 18. Which type of compressor is most common in residential split systems? A. Screw B. Scroll C. Centrifugal D. Reciprocating
B. Hearing protection only C. Steel-toe boots only D. Welding mask Answer: A. Safety glasses and gloves Explanation: Refrigerants can cause frostbite and eye injury; PPE is required under OSHA standards.
23. A duct leakage test is primarily used to: A. Detect refrigerant loss B. Measure electrical efficiency C. Check for air loss in ductwork D. Verify thermostat accuracy Answer: C. Check for air loss in ductwork Explanation: Duct leakage wastes energy and reduces comfort; blower door or duct blaster tests are used. 24. What is the typical high-side operating pressure for R-410A at 95°F ambient? A. 120–150 psig B. 220–250 psig C. 320–360 psig D. 400–450 psig Answer: C. 320–360 psig Explanation: R-410A operates at higher pressures than R-22; around 340 psig is common at 95°F ambient. 25. In Nevada, outdoor condensing units must be installed on: A. Bare soil B. Wood pallets C. Level concrete or approved pad D. Rooftop only Answer: C. Level concrete or approved pad Explanation: Code requires a stable, level base to prevent vibration and ensure drainage.
26. What is the function of a crankcase heater in a compressor? A. Increase cooling capacity B. Prevent refrigerant migration into the oil C. Improve condenser efficiency D. Speed up defrost cycles Answer: B. Prevent refrigerant migration into the oil Explanation: It keeps oil warm, preventing refrigerant from condensing inside the crankcase. 27. A dirty air filter can cause: A. Low suction pressure and coil icing B. High suction pressure C. Reduced head pressure only D. Compressor overheating only Answer: A. Low suction pressure and coil icing Explanation: Reduced airflow causes refrigerant to overcool, leading to ice formation on the evaporator. 28. Which code governs refrigerant piping installation in Nevada? A. National Plumbing Code B. International Mechanical Code (IMC) C. Uniform Electrical Code D. Uniform Building Code only Answer: B. International Mechanical Code (IMC) Explanation: Nevada adopts the IMC for HVAC system installation requirements. 29. What does a TXV do when load increases? A. Closes to reduce refrigerant flow B. Opens to increase refrigerant flow C. Shuts off completely D. Increases head pressure
33. What type of refrigerant oil is used with R- 410A? A. Mineral oil B. Alkylbenzene oil C. POE (Polyolester) oil D. PAG oil Answer: C. POE (Polyolester) oil Explanation: POE oil is required for HFC refrigerants like R-410A due to miscibility. 34. A system is short cycling. One possible cause is: A. Oversized system B. Undersized ductwork C. Low blower speed D. All of the above Answer: D. All of the above Explanation: Any airflow or sizing mismatch can cause the system to satisfy the thermostat too quickly. 35. The low-pressure switch in a system protects against: A. Compressor overheating B. Loss of refrigerant or airflow blockage C. Electrical surges D. Excessive humidity Answer: B. Loss of refrigerant or airflow blockage Explanation: It shuts off the compressor to prevent damage when suction pressure drops too low. 36. What is the typical lifespan of a residential split system in Nevada? A. 5–8 years B. 10–15 years C. 20–25 years D. 30 years Answer: B. 10–15 years Explanation: Desert heat can shorten lifespan; regular maintenance extends it.
37. Which of the following is a must when lifting heavy condensing units? A. Use a single technician for speed B. Use proper lifting equipment or team lift C. Remove refrigerant before moving D. Tilt unit on its side Answer: B. Use proper lifting equipment or team lift Explanation: Prevents injury and equipment damage; OSHA requires safe lifting practices. 38. What is the main advantage of a variable-speed blower motor? A. Cheaper than PSC motors B. Adjusts airflow for efficiency and comfort C. Uses higher amperage D. Works only at full speed Answer: B. Adjusts airflow for efficiency and comfort Explanation: ECM motors modulate speed to match demand, improving comfort and efficiency. 39. Which is the first step in troubleshooting an AC unit that won’t start? A. Replace the compressor B. Check power supply and breakers C. Replace refrigerant D. Adjust the TXV Answer: B. Check power supply and breakers Explanation: Always start with the simplest and safest checks before replacing components. 40. The condenser fan draws air: A. Through the sides and out the top B. Through the top and out the sides C. From the bottom and out the top D. From the top and out the bottom
B. 5/8"
C. 3/4"
D. 7/8"
Answer: B. 5/8" Explanation: Manufacturer specs determine exact sizing; 5/8" is typical for 2 - ton up to moderate runs.
45. Which tool is used to check airflow in CFM? A. Micrometer B. Anemometer C. Clamp-on ammeter D. Psychrometer Answer: B. Anemometer Explanation: Anemometers measure air velocity, which is used to calculate CFM. 46. Which type of solder is acceptable for potable water lines but NOT refrigerant lines? A. Lead-free solder B. 95/5 solder C. Silver brazing alloy D. Soft solder Answer: D. Soft solder Explanation: Refrigerant lines require brazing alloys with higher strength and melting points. 47. A high subcooling reading often indicates: A. Low refrigerant charge B. Overcharged system or restricted liquid line C. Dirty evaporator D. Short cycling Answer: B. Overcharged system or restricted liquid line Explanation: Too much refrigerant or blockage traps liquid in the condenser.
48. The term “plenum” in HVAC refers to: A. The refrigerant return pipe B. The duct section that connects to the air handler C. The electrical control box D. The outdoor unit housing Answer: B. The duct section that connects to the air handler Explanation: Plenums distribute air from the handler to branch ducts. 49. What is the required clearance above an air-cooled condenser for proper airflow? A. 6 inches B. 12 inches C. 24 inches D. 48 inches Answer: C. 24 inches Explanation: Manufacturer specs vary; 24" above is a common minimum for vertical discharge. 50. A mismatched indoor and outdoor coil set can cause: A. Reduced efficiency and capacity B. Improved SEER rating C. Lower head pressure D. Easier maintenance Answer: A. Reduced efficiency and capacity Explanation: Mismatched coils can lead to poor performance, moisture problems, and warranty voiding. 51. What is the recommended slope for horizontal condensate drain lines? A. 1/4" per foot B. 1/8" per foot C. 1/2" per foot D. Level
B. Dirty condenser coil or blocked airflow C. Low ambient temperature D. Low refrigerant charge Answer: B. Dirty condenser coil or blocked airflow Explanation: Restricting heat rejection raises discharge pressure.
56. The IMC requires duct insulation in unconditioned spaces with a minimum R-value of: A. R- 2 B. R-4. C. R- 6 D. R- 8 Answer: C. R- 6 Explanation: For most residential applications in Nevada, R-6 is the minimum duct insulation in unconditioned areas. 57. A PSC blower motor that won’t start may have a: A. Bad start relay B. Bad run capacitor C. Faulty high-limit switch D. Bad contactor Answer: B. Bad run capacitor Explanation: PSC motors rely on the run capacitor for starting and running torque. 58. Which component removes moisture from refrigerant in a system? A. Sight glass B. Filter-drier C. TXV D. Suction accumulator Answer: B. Filter-drier Explanation: It contains desiccant to absorb moisture and prevent acid formation.
59. When evacuating a system, what indicates moisture is present? A. Pressure rises quickly after pump shut-off B. Pressure remains constant C. Temperature drop in suction line D. High superheat Answer: A. Pressure rises quickly after pump shut-off Explanation: Moisture boils off, increasing pressure during a standing vacuum test. 60. Which refrigerant has the highest operating pressures? A. R-134a B. R-410A C. R-22 D. R-407C Answer: B. R-410A Explanation: R-410A operates at approximately 60% higher pressures than R-
61. Which type of control uses a bimetal element to sense temperature? A. Electronic thermostat B. Mercury switch C. Mechanical thermostat D. Solid-state relay Answer: C. Mechanical thermostat Explanation: A bimetal strip bends with temperature change to make or break a circuit. 62. The purpose of a suction line accumulator is to: A. Store excess refrigerant during low load B. Prevent liquid refrigerant from entering the compressor C. Maintain constant suction pressure D. Increase subcooling
Answer: B. Remove heat from refrigerant vapor Explanation: This cools and condenses the vapor back to liquid.
67. A float switch in a condensate pan: A. Starts the compressor B. Stops the system if water backs up C. Adjusts blower speed D. Opens TXV under load Answer: B. Stops the system if water backs up Explanation: Prevents overflow damage when the drain is clogged. 68. What tool is used to remove and install valve cores in service ports? A. Manifold gauge B. Valve core removal tool C. Torque wrench D. Schrader key Answer: B. Valve core removal tool Explanation: This allows replacing cores without losing refrigerant. 69. What is the purpose of measuring subcooling? A. Determine evaporator performance B. Check condenser performance and charge level C. Measure air temperature rise D. Test thermostat calibration Answer: B. Check condenser performance and charge level Explanation: High subcooling may mean overcharge; low may mean undercharge. 70. Which wire color is typically used for the 24V common in HVAC systems? A. Red B. Yellow C. Blue D. Green
Answer: C. Blue Explanation: Blue is standard for the common wire, though it can vary.
71. What is the correct PPE for working in attics during summer in Nevada? A. Hard hat only B. Lightweight clothing, gloves, eye protection, respirator if dusty C. Heavy winter coat D. Rain gear Answer: B. Lightweight clothing, gloves, eye protection, respirator if dusty Explanation: Heat stress prevention and dust protection are priorities. 72. Which refrigerant is considered a high-pressure refrigerant under EPA definitions? A. R-22 B. R-410A C. R-134a D. R- 123 Answer: B. R-410A Explanation: High-pressure category includes R-410A due to operating pressures above 170 psig at 104°F. 73. What is the primary purpose of an economizer in a commercial HVAC system? A. Increase heating efficiency B. Use cool outdoor air for free cooling C. Increase refrigerant charge D. Reduce airflow Answer: B. Use cool outdoor air for free cooling Explanation: Economizers reduce mechanical cooling load by using outdoor air. 74. The NEC requires flexible conduit for outdoor condenser connections to allow:
