With the mode knob in the VENT position, the vent valve opens and air flows to the instrument panel outlet ducts.

With the mode knob in the BLEND position between the HEATER and the VENT modes, the vent valve moves to an intermediate range uncovering more of the opening to the instrument panel vents. This valve movement results in increased airflow to the vent nozzles and decreased airflow to the heater duct.

With the mode knob in the HEATER position, the vent valve is partially closed. The defroster valve also remains closed. As a result, the air from the blower fan is heated as necessary and directed to the defroster valve. The defroster valve then sends most of the airflow to the heater duct and some to the defroster nozzle.

With the mode knob in the BLEND position between the HEATER and DEFROST modes, the defroster valve moves to an intermediate range uncovering more of the opening to the defroster. As a result, airflow to the defroster nozzle is increased, and airflow to the heater duct is decreased.

With the mode knob in the DEFROST position, the defroster valve moves to fully uncover the opening to the defroster nozzle. The valve simultaneously restricts the opening to the heater duct. This movement delivers maximum airflow to the defroster nozzle, while allowing only a small amount of airflow to the heater duct.