InterNACHI HVAC Systems Analysis 3 — Questions and Answers
Question 1: What is the purpose of an expansion valve (TXV) in a refrigeration circuit?
- To compress refrigerant to high pressure
- To meter refrigerant flow and reduce pressure before the evaporator (Correct answer)
- To reverse refrigerant direction in heat pump mode
- To separate liquid and vapor refrigerant
Correct answer: To meter refrigerant flow and reduce pressure before the evaporator
The thermostatic expansion valve meters refrigerant into the evaporator coil, dropping pressure so the refrigerant can absorb heat effectively.
Question 2: Which duct condition most significantly reduces HVAC system efficiency and should be documented during inspection?
- Flexible duct with minor bends
- Uninsulated ducts in unconditioned attic space (Correct answer)
- Round metal ducts with screwed connections
- Supply registers mounted in the floor
Correct answer: Uninsulated ducts in unconditioned attic space
Uninsulated ducts in an unconditioned attic can lose 25–40% of conditioned air energy to the surrounding environment, significantly degrading system efficiency.
Question 3: What is the minimum clearance typically required around an outdoor condensing unit for proper airflow?
- 6 inches on all sides
- 12–18 inches on all sides with 4–5 feet above (Correct answer)
- 24 inches on all sides with 8 feet above
- 36 inches on all sides with 10 feet above
Correct answer: 12–18 inches on all sides with 4–5 feet above
Most manufacturers require at least 12–18 inches of clearance on the sides and 4–5 feet of unobstructed space above the condenser for adequate airflow.
Question 4: A homeowner reports that one room is always too hot in summer despite the AC running. Which inspection finding is most likely the cause?
- Oversized condensing unit
- Blocked or disconnected supply duct to that room (Correct answer)
- Dirty condenser coil outdoors
- Thermostat located in a sunny location
Correct answer: Blocked or disconnected supply duct to that room
A blocked or disconnected supply duct prevents conditioned air from reaching the room, creating an uneven temperature condition throughout the home.
Question 5: What refrigerant has been used as the primary replacement for R-22 in residential air conditioning systems since 2010?
- R-410A (Correct answer)
- R-134a
- R-32
- R-407C
Correct answer: R-410A
R-410A became the dominant replacement refrigerant for R-22 in residential systems due to its higher efficiency and zero ozone depletion potential.
Question 6: Which safety control shuts down a gas furnace when the heat exchanger overheats?
- Pressure switch
- Limit switch (high-limit control) (Correct answer)
- Flame sensor
- Draft inducer relay
Correct answer: Limit switch (high-limit control)
The limit switch monitors heat exchanger temperature and shuts off the burners if the temperature exceeds a safe threshold, preventing overheating and potential fires.
Question 7: When inspecting a gravity (non-forced air) warm-air furnace, what is the primary concern an inspector should note?
- Lack of electronic ignition
- Age and condition of the heat exchanger, which is difficult to inspect and often deteriorated (Correct answer)
- Absence of a programmable thermostat
- Low AFUE efficiency rating
Correct answer: Age and condition of the heat exchanger, which is difficult to inspect and often deteriorated
Gravity furnaces are typically very old, and their large cast-iron heat exchangers are prone to cracking, creating a serious carbon monoxide hazard that warrants specialist evaluation.
InterNACHI HVAC Systems Analysis 3
What is the purpose of an expansion valve (TXV) in a refrigeration circuit?