It's a very basic system. Hot air from the fan flows thru pipes to front of bus. There are four levers on the dash. Two are for fresh air the other two are for the heater. Cables run from the heater levers to flaps that open and close letting the hot air from the fan housing flow to the front of the bus to you feet or the windshield for defrosting. There is a lever to the right of the gas petal push it up and get warm air to your feet and down to defrost the window. In the winter you will have to drive a few miles before getting warm air from the heater. (I carry a blanket for non-hardy passengers) If the cables are old they can be replaced by running new cables beside the old ones. The flaps are located on each underside of the bus by the back tires.