If you hear unusual noises such as rattling, buzzing, or whistling, it can signal loose or damaged parts. Inconsistent temperatures across different rooms might indicate an air conditioning issue, while weak or uneven airflow could be a sign of fan problems or obstructions in the ductwork.
A sudden increase in energy bills without a change in usage may mean the system is running inefficiently. Musty or burning smells can be a sign of mold growth or electrical issues, and any issues with the thermostat, such as unresponsiveness or erratic heating or cooling, should be inspected by a professional.
If your HVAC system is frequently cycling on and off, it may be improperly sized or have a mechanical problem. Humidity problems, such as overly dry or moist indoor air, may also indicate a need for servicing. Water leaks or pooling around the unit, an increase in dust or allergens inside the home, or visible wear and tear on the equipment, including frayed wires or corrosion, are all signs that servicing is needed.
Finally, the age of the system plays a role, with older systems requiring more frequent checks and maintenance.