InterNACHI - International Association of Certified Home Inspectors HVAC Systems Analysis Questions and Answers — Questions and Answers
Question 1: While inspecting a central air conditioning system on a warm day, an inspector observes a significant amount of ice on the evaporator coil and the suction line. Which of the following is the most likely cause of this condition?
- The system is oversized for the home.
- The thermostat is set to a very low temperature.
- Restricted airflow across the evaporator coil or a low refrigerant charge. (Correct answer)
- The outdoor condenser unit is dirty and cannot reject heat effectively.
Correct answer: Restricted airflow across the evaporator coil or a low refrigerant charge.
Ice formation on the evaporator coil and suction line during cooling mode is a classic symptom of the coil becoming too cold (dropping below 32°F). This is typically caused by either insufficient warm air moving across the coil to be absorbed or a low refrigerant level, which causes a pressure drop and excessive cooling. A dirty filter is a common cause of restricted airflow.
Question 2: What does the Annual Fuel Utilization Efficiency (AFUE) rating of a furnace represent?
- The speed at which the furnace can heat a space, measured in BTUs per hour.
- The percentage of fuel consumed that is converted into usable heat for the home over a year. (Correct answer)
- The cooling efficiency of the system when paired with an air conditioner.
- The effectiveness of the furnace's air filtration system.
Correct answer: The percentage of fuel consumed that is converted into usable heat for the home over a year.
AFUE stands for Annual Fuel Utilization Efficiency and is a standardized measure of how efficiently a furnace converts its fuel source (like gas or oil) into heat over an entire heating season. An AFUE of 95% means that 95 cents of every dollar spent on fuel is converted to heat, while the other 5 cents are lost, typically through the flue.
Question 3: Which of the following represents the MOST significant life-safety hazard associated with a cracked heat exchanger in a gas-fired furnace?
- A significant decrease in the furnace's heating efficiency.
- The furnace may overheat and shut down on a safety limit switch.
- The potential for combustion gases, like carbon monoxide, to mix with the circulated household air. (Correct answer)
- Loud banging or popping noises during furnace operation.
Correct answer: The potential for combustion gases, like carbon monoxide, to mix with the circulated household air.
The primary and most critical danger of a cracked heat exchanger is the breach in separation between the combustion chamber and the breathable air supply. This can allow toxic flue gases, most notably carbon monoxide (CO), to enter the ductwork and be distributed throughout the home, creating a life-threatening situation.
Question 4: During an attic inspection, you observe flexible ductwork that is compressed in several areas and has multiple sharp 90-degree bends. What is the primary defect to report?
- The ductwork is not adequately insulated for an attic application.
- The ductwork material is not approved for residential use.
- The sharp bends and compression severely restrict airflow, reducing system performance and efficiency. (Correct answer)
- The flexible ductwork should be replaced with rigid metal ducting.
Correct answer: The sharp bends and compression severely restrict airflow, reducing system performance and efficiency.
Flexible ductwork must be installed with gentle bends (radius greater than one duct diameter) and without compression to ensure proper airflow. Sharp bends and kinks create significant friction and turbulence, which chokes off the airflow, leading to poor heating/cooling performance, wasted energy, and strain on the HVAC equipment.
Question 5: An inspector is examining the refrigerant lines connected to an outdoor condenser unit. One line is larger in diameter, insulated, and feels cool to the touch while the system is operating in cooling mode. This line is known as the:
- Suction line (Correct answer)
- Liquid line
- Discharge line
- Condensate line
Correct answer: Suction line
The larger, insulated copper line is the suction line (or vapor line). It carries cool, low-pressure refrigerant in a gaseous state from the indoor evaporator coil back to the outdoor compressor. It is insulated to prevent it from absorbing excess heat from the ambient air, which would decrease the system's efficiency.
Question 6: What is the primary function of a condensate trap on the drain line of an indoor air handler coil?
- To prevent insects and pests from entering the unit through the drain line.
- To create a water seal that prevents air from being drawn into or blown out of the unit through the drain. (Correct answer)
- To measure the amount of water being removed from the air.
- To provide a convenient location for adding cleaning tablets to the system.
Correct answer: To create a water seal that prevents air from being drawn into or blown out of the unit through the drain.
A condensate trap holds a small amount of water to create a seal. In an air handler where the coil is under negative pressure (before the blower), this seal prevents unconditioned air from being sucked into the unit through the drain line. In a furnace where the coil is under positive pressure (after the blower), it prevents conditioned air from being blown out. This ensures proper drainage and maintains system efficiency.
InterNACHI - International Association of Certified Home Inspectors HVAC Systems Analysis Questions and Answers
While inspecting a central air conditioning system on a warm day, an inspector observes a significant amount of ice on the evaporator coil and the suction line.
Which of the following is the most likely cause of this condition?