The base heater system is designed to provide heating, ventilation, windshield defrosting, side window defogging, and on some vehicles, heating directly to the rear seat area.
The heater and fan assembly blower regulates the airflow from the air inlet for further processing and distribution.
The heater core transfers the heat from the engine coolant to the inlet air.
The temperature door regulates the amount of the air that passes through the heater core. The temperature door also controls the temperature of the air by controlling the mix of the heated air and the ambient air.
The mode door regulates the flow and the distribution of the processed air to the heater ducts and to the defroster ducts.