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Question 1. Which method of heat transfer requires a temperature gradient and a material medium to occur? A) Radiation B) Convection C) Conduction D) Phase change Answer: C Explanation: Conduction moves thermal energy through a solid or stationary fluid via molecular vibration caused by a temperature difference. Question 2. In a psychrometric chart, the line that represents constant wet-bulb temperature is always: A) Horizontal B) Vertical C) Diagonal sloping upward to the right D) Curved and parallel to the saturation curve Answer: C Explanation: Wet-bulb lines slope upward to the right because as dry-bulb temperature rises, the same wet-bulb temperature corresponds to higher enthalpy and lower relative humidity. Question 3. According to the International Mechanical Code (IMC), the minimum clearance required in front of a gas-fired furnace for service access is: A) 12 inches B) 24 inches C) 36 inches
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D) 48 inches Answer: B Explanation: IMC Section 603.2.1.2 requires at least 24 in. of clear space in front of the furnace for inspection and maintenance. Question 4. Which OSHA regulation specifically addresses lockout/tagout (LOTO) procedures for mechanical equipment? A) 29 CFR 1910. B) 29 CFR 1926. C) 29 CFR 1910. D) 29 CFR 1910. Answer: A Explanation: OSHA standard 29 CFR 1910.147 covers the control of hazardous energy (LOTO) for all machines and equipment. Question 5. In a gas-fired furnace, a Category III venting system is characterized by: A) Direct vent to the outdoors with a sealed combustion chamber. B) Natural draft with a chimney. C) Exhaust gas temperature above 1,000 °F. D) Exhaust gas temperature below 500 °F and use of a vent pipe of at least 4 in. diameter. Answer: D Explanation: Category III venting allows lower exhaust gas temperatures (< 500 °F) and uses a minimum 4-in. vent pipe, typically for atmospheric-type furnaces.
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D) R-454B
Answer: C Explanation: R-22 (chlorodifluoromethane) has a GWP of ~1,810, higher than R-32 (~677), R-410A (~2,088 but phased out), and R-454B (~1,020). However, compared to modern low-GWP options, R-22 is the highest among listed. Question 9. In a low-voltage thermostat wiring diagram, the “C” wire is used for: A) Cooling call. B) Common return for power. C) Controlling fan speed. D) Connecting to the compressor. Answer: B Explanation: The “C” (common) wire provides a continuous 24 V return path to power the thermostat. Question 10. A PSC (Permanent Split Capacitor) motor differs from a capacitor-start motor primarily because: A) It uses a permanent split phase winding for starting torque. B) It requires a centrifugal switch. C) It has a start capacitor that disconnects after start. D) It cannot run at variable speeds. Answer: A Explanation: PSC motors have a start winding permanently connected through a run capacitor, eliminating the need for a start capacitor or centrifugal switch. Question 11. The term “superheat” in a refrigerant system refers to:
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A) The temperature difference between the refrigerant gas and its saturation temperature at the same pressure. B) The amount of heat removed from the evaporator coil. C) The temperature rise across the condenser. D) The latent heat absorbed during phase change. Answer: A Explanation: Superheat is the temperature of vapor above its saturation (boiling) point at a given pressure, indicating how much extra heat the vapor carries. Question 12. Which of the following duct materials is most resistant to moisture absorption and suitable for indoor residential applications? A) Fiberglass duct board B) Galvanized steel C) Flexible aluminum duct D) PVC duct Answer: B Explanation: Galvanized steel does not absorb moisture, making it ideal for indoor ductwork where condensation may occur. Question 13. In Manual D duct design, the “equal friction” method assumes: A) All ducts have the same pressure loss per unit length regardless of size. B) Velocity is constant throughout the system. C) Friction loss is proportional to duct surface area. D) Ducts are sized to achieve the same pressure drop per 100 ft of length. Answer: D
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C) Safety glasses, gloves, and flame-resistant clothing. D) Earplugs and respirator. Answer: C Explanation: OSHA mandates safety glasses, gloves, and flame-resistant clothing when dealing with high-pressure cylinders to protect against impact, cold burns, and potential leaks. Question 17. In a hydronic heating system, a “two-pipe” configuration means: A) One pipe supplies hot water and the other returns cooled water to the boiler. B) Two separate loops for heating and cooling. C) One pipe for water and one for refrigerant. D) Two parallel supply lines for redundancy. Answer: A Explanation: Two-pipe systems have distinct supply and return lines, allowing water to flow from the boiler to the heat emitters and back. Question 18. The term “latent heat” in HVAC refers to: A) Heat required to raise the temperature of a substance. B) Heat absorbed or released during a phase change without a temperature change. C) Heat lost due to duct leakage. D) Heat generated by combustion. Answer: B Explanation: Latent heat is the energy involved in a phase transition (e.g., liquid to vapor) at constant temperature.
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Question 19. Which of the following is a requirement for a mechanical permit under most municipal codes? A) Submission of a load calculation report. B) Installation of a programmable thermostat. C) Use of only copper piping. D) Presence of a fire sprinkler system. Answer: A Explanation: Mechanical permits typically require documentation such as load calculations (Manual J) to verify system sizing. Question 20. In a scroll compressor, the primary advantage over a reciprocating compressor is: A) Higher noise level. B) More moving parts. C) Greater efficiency and smoother operation. D) Ability to handle larger refrigerant charges. Answer: C Explanation: Scroll compressors have fewer moving parts, resulting in higher efficiency, lower noise, and smoother operation. Question 21. The “dry-bulb temperature” measured by a standard thermometer is: A) The temperature of air after removing moisture. B) The temperature of air without any influence from humidity. C) The same as wet-bulb temperature under all conditions. D) The temperature of the evaporated refrigerant.
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A) The difference between motor speed and synchronous speed. B) The voltage drop across the drive. C) The amount of current draw during start-up. D) The time delay before the motor stops. Answer: A Explanation: Slip is the difference between the rotating magnetic field speed (synchronous) and the actual rotor speed in an induction motor. Question 25. A “capillary tube” used as a metering device in a refrigeration system is best described as: A) A variable orifice that adjusts flow automatically. B) A fixed-diameter tube that provides a pressure drop based on refrigerant flow. C) A high-capacity expansion valve. D) A type of accumulator. Answer: B Explanation: Capillary tubes have a fixed internal diameter; the pressure drop across them creates the required flow restriction. Question 26. According to the Uniform Mechanical Code (UMC), the minimum clearance between a gas pipe and combustible material is: A) 1 in. B) 2 in. C) 3 in. D) 4 in. Answer: B
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Explanation: UMC Section 603.2.2 requires at least 2 in. clearance from gas piping to combustible surfaces. Question 27. The purpose of a “drip leg” in a fuel-gas piping system is to: A) Increase pressure. B) Capture condensate and prevent water from entering appliances. C) Reduce turbulence. D) Provide a location for pressure testing. Answer: B Explanation: Drip legs collect moisture and debris, protecting downstream equipment from liquid ingress. Question 28. In a forced-air furnace, the “static pressure” measured at the blower outlet is used to evaluate: A) Temperature rise across the heat exchanger. B) Airflow resistance and blower performance. C) Fuel pressure. D) Refrigerant superheat. Answer: B Explanation: Static pressure indicates the resistance the blower must overcome; it helps assess duct design and blower sizing. Question 29. Which of the following best describes the function of a “sensible heat” load in HVAC calculations? A) Heat associated with moisture removal. B) Heat that changes temperature without changing moisture content.
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Question 32. The “refrigerant charge” in a split-system air conditioner is typically measured in: A) Pounds (lb) or kilograms (kg). B) Cubic feet (cf). C) Gallons (gal). D) BTU/hr. Answer: A Explanation: Refrigerant quantity is expressed as mass, commonly in pounds or kilograms. Question 33. Which of the following is a common symptom of a low-superheat condition in a refrigerant system? A) High compressor discharge temperature. B) Flooded evaporator coil. C) Low suction pressure. D) Excessive outdoor fan speed. Answer: B Explanation: Low superheat means insufficient vapor leaving the evaporator; liquid can flood the compressor, indicating a flooded evaporator. Question 34. The “fan-powered” versus “induced-draw” classification of kitchen hoods refers to: A) The presence of a mechanical fan in the hood. B) Whether the hood relies on the cooking equipment’s exhaust. C) The type of filter used. D) The material of the hood construction.
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Answer: A Explanation: Fan-powered hoods have an integral blower, while induced-draw hoods use the building’s exhaust system to move air. Question 35. In a typical residential HVAC system, the thermostat’s “Y” terminal is connected to: A) The fan relay. B) The compressor/contactors. C) The heat pump’s reversing valve. D) The auxiliary heat strip. Answer: B Explanation: The “Y” terminal signals the cooling stage, energizing the compressor contactor. Question 36. Which of the following statements about “laminar flow” in ducts is true? A) It occurs at high Reynolds numbers. B) It results in higher pressure losses than turbulent flow. C) It is characterized by smooth, parallel streamlines. D) It is desirable for high-velocity air distribution. Answer: C Explanation: Laminar flow has smooth, orderly layers with low mixing, unlike turbulent flow. Question 37. The purpose of an “oil safety control” (OSC) in a compressor is to: A) Prevent oil leakage into the refrigerant.
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Question 40. In a water-cooled chiller, the “condenser water pump” is primarily responsible for: A) Pressurizing refrigerant. B) Circulating water through the condenser coil. C) Providing makeup water to the system. D) Controlling condenser temperature. Answer: B Explanation: The pump moves water through the condenser, removing heat from the refrigerant. Question 41. Which of the following is a required safety feature for a furnace equipped with a standing pilot? A) A flame sensor. B) A high-limit switch. C) An electronic ignition module. D) A pressure relief valve. Answer: B Explanation: A high-limit (or high-temperature) switch shuts down the furnace if the burner or heat exchanger exceeds safe temperatures. Question 42. The “Manual J” calculation is used to determine: A) Duct sizing. B) Heating and cooling loads for a building. C) Boiler water volume.
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D) Refrigerant charge. Answer: B Explanation: Manual J is the industry-standard method for calculating residential heating and cooling loads. Question 43. When performing a combustion analysis on a gas furnace, a high CO₂ reading typically indicates: A) Incomplete combustion. B) Excess air in the combustion process. C) A cracked heat exchanger. D) A faulty thermostat. Answer: B Explanation: High CO₂ suggests too much excess air, diluting the combustion gases; incomplete combustion would raise CO rather than CO₂. Question 44. The term “static pressure” in a duct system is measured in: A) Inches of water gauge (in. wg). B) Pounds per square foot (psf). C) Pascals (Pa). D) Both A and C are acceptable. Answer: D Explanation: Static pressure can be expressed in inches of water gauge or Pascals; both are common units. Question 45. Which of the following is the most common cause of a “short-cycling” furnace?
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Explanation: Refrigerants are electrical hazards; Class C (CO₂) extinguishers are suitable for non-combustible, electrically energized equipment. Question 48. A “heat exchanger” in a furnace primarily serves to: A) Convert electrical energy to heat. B) Transfer heat from combustion gases to the circulating air. C) Store thermal energy for later use. D) Regulate refrigerant pressure. Answer: B Explanation: The heat exchanger separates combustion gases from the air stream while transferring heat. Question 49. The term “blower door” in HVAC testing refers to: A) A door on the furnace that allows access to the blower motor. B) A calibrated panel used to measure building airtightness. C) A safety interlock on the compressor. D) The door on a commercial refrigeration unit. Answer: B Explanation: A blower-door test measures the infiltration rate and airtightness of a building. Question 50. In a pneumatic control system, the “3-wire” configuration for a solenoid valve typically includes: A) Two power wires and one signal wire. B) One power, one ground, and one control (coil) wire.
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C) Three-phase power connections. D) Two sensor wires and one actuator wire. Answer: B Explanation: A 3-wire solenoid valve has a power (line), ground (neutral), and a control wire that energizes the coil. Question 51. Which of the following is a primary advantage of using CSST (Corrugated Stainless Steel Tubing) for fuel-gas distribution? A) Higher pressure rating Question 53. Under the Uniform Mechanical Code, the minimum pipe size for a natural-gas service line feeding a 75 000 BTU/hr furnace, using ½ in. CSST, is: A) ¼ in. B) ½ in. C) ¾ in. D) 1 in. Answer: B Explanation: The UMC permits ½ in. CSST to carry up to 100 000 BTU/hr at typical residential pressures, making it the minimum required size for a 75 000 BTU/hr furnace. Question 54. A “safety relief valve” on a water-heater must be set to open at a pressure not exceeding: A) 120 % of the design pressure. B) 150 % of the design pressure. C) 200 % of the design pressure. D) 250 % of the design pressure.
