The HVAC system is part of the four main systems you want to know are working properly or would want to know of any repairs that need to be made before purchasing a property. This component if defected, could cost you a high dollar amount if left unknown. The inspector will look at your furnace and A/C unit to ensure it is working properly. They will turn the systems on to see if they are starting up correctly and working, will check vents for proper air flow and check the thermostat for working conditions as well.