Which of the following is a common sign of HVAC system malfunction?

Unusual noises and insufficient heating or cooling are clear indicators of an HVAC system malfunction. When a system is operating correctly, it should run smoothly and quietly. If an HVAC system begins to produce strange sounds—such as banging, hissing, or grinding—it often signals that there are mechanical issues, such as a failing blower motor, loose components, or debris obstructing the fan.

Insufficient heating or cooling also points to potential system problems. If a homeowner notices that their space isn't reaching the expected temperature, this can indicate issues such as a refrigerant leak, a malfunctioning compressor, or problems with the ductwork that prevents adequate airflow. Recognizing these signs early can help in diagnosing problems and ultimately lead to effective repairs, ensuring the system operates efficiently.

The other choices reflect either normal operation or maintenance practices rather than malfunction indicators. Regular energy costs and consistent temperature control suggest that the system is functioning properly. Frequent air filter replacement is important for maintaining air quality and system efficiency but does not directly indicate a malfunction. Understanding these distinctions is crucial in effective HVAC troubleshooting and maintenance.