I completed a real estate inspection on an air conditioner. I visually inspected the unit. The blower wheel was dusty, checked the air return filter and it was dirty and needed replaced. Also discovered that the system was low on charge. I also performed a inspection on the gas furnace and discovered that the heat exchanger had a bit of carbon build up and the humidifier pad needs replaced. Informed customer of all of these things but over all the systems were working at the time of departure.