Which activity should be performed during a routine home inspection regarding the HVAC system?

During a routine home inspection, testing the thermostat functions is essential as it helps determine whether the HVAC system is operating correctly. The thermostat regulates the temperature by signaling the HVAC system to heat or cool the home as needed. If the thermostat is malfunctioning, it can lead to inadequate heating or cooling, impacting the comfort of the inhabitants and potentially leading to higher energy bills or further HVAC issues.

While changing air filters is a good maintenance practice, it is typically the homeowner's responsibility and not something that is done during an inspection. Cleaning air ducts might improve air quality, but it is also a maintenance task that does not fall under the scope of a standard home inspection. Inspecting refrigerant levels usually requires specialized equipment and expertise beyond a routine inspection, making it unnecessary for the standard evaluation. Hence, testing the thermostat functions is the most appropriate and immediate activity to assess the HVAC system's performance during a home inspection.