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

A common sign of a malfunctioning HVAC system is the presence of unusual noises emanating from the unit. These noises may indicate underlying issues, such as loose or damaged components, which can compromise the system's efficiency and operation. For instance, rattling sounds might suggest loose panels or ductwork, while grinding noises could point to problems with the motor or fan. Recognizing these auditory warnings is crucial for timely maintenance, as they can prevent more significant and costly repairs if addressed promptly.

In contrast, consistent temperatures throughout the building and optimal air quality are indicators of a well-functioning HVAC system. Low energy costs can also reflect efficient operation, suggesting the system is running effectively. If any of these situations are present, it typically indicates that the HVAC system is functioning correctly rather than malfunctioning. Therefore, unusual noises stand out as a definitive sign of potential trouble within the system.