Handbook 752 Air Conditioning and Climate Control Heating System Automobiles use the hot coolant circulating in the engine to warm the passenger cabin. Heater hoses connected to the engine’s cooling system circulate heated coolant through the heater core. The heater core is a heat exchanger similar to a radiator. A blower fan pushes air through the air spaces in the heater core where the air absorbs heat. The heated air is then sent through air ducts to the cabin. Components To turn the heat off and on, earlier models used a heater control valve to regulate the flow of water into the heater core. When the valve is partially open, the hot water flows slowly through the heater core.
As the air passes through the heater core, it cools the water. The result is mildly warmed air. When the valve is fully open, the hot water flows rapidly through the heater core. The water doesn’t have as much time to cool, so the air flowing into the cabin is warmer. Most current systems use a blend door to vary the amount of heat flowing into the cabin, rather than a heater control valve. The blower typically has several fan speeds to regulate air flow into the cabin for passenger comfort. One disadvantage of a simple heating system such as this is it provides no heat until the engine has sufficiently warmed the engine coolant. 10 Technical Training