The hot fluid also called coolant is also used to provide heat to the interior of the vehicle whenever such is needed. This operates on a simple and straight forward system that is inclusive of a heater core, which looks like a small version of a radiator, linked to the cooling system with a pair of rubber hoses. One hose gets hot coolant from the water pump to the heater core and the other hose sends the coolant to the top of the engine. There is usually a heater control valve in one of the hoses to prevent the flow of coolant into the heater core when maximum air conditioning is required.
A fan, always referred to as a blower, draws air through the heater core and directs it through the heater ducts to the interior of the car. Temperature of the heat is modulated by a blend door that mixes cool outside air, or sometimes air conditioned air with the heated air coming through the heater core. This blend door allows control of the temperature of the air coming into the interior. Other doors allows the directing of the warm air through the ducts on the floor, the defroster ducts at the base of the windshield, and the air conditioning ducts located in the instrument panel
SEE ALSO:WHY WOULD A CAR ENGINE OVERHEAT