Heater Core: Description and Operation

The heater core is continuously supplied by hot engine coolant. When heat is not required, the air bypasses the heater core. The heater reaches its maximum output when all the air flows through the heater core (the A/C temperature control lever is to the right) and the blower motor control is at the HIGH position. Usually, heated air is blended with fresh air for comfort.

Heated air in the vehicle provides:

^ Wintertime comfort
^ Windshield defrosting
^ Windshield defogging in high humidity
^ Summertime temperature control with air conditioning (if equipped)

Heat input to the air varies with a portion of the air routed by the temperature blend door either through or around the heater core. In cooling, the ventilated air passes through the evaporator (A/C option only) where it is dehydrated by cooling before it is reheated in the heater core provide to a comfortable temperature level.