Heater and Defroster Valves

The heater and defroster valves are operated by a three-position defroster valve vacuum actuator attached to the defroster valve, which is in-turn connected by a link to the heater valve. When the defroster valve vacuum actuator is in the at rest (no vacuum) position, a blend of air is directed to the defroster and the floor outlets; as in DEFOG mode. When vacuum is applied to the lower side of the defroster valve vacuum actuator, the defroster valve is opened (full-down) and the heater valve is closed (full-down), allowing air to be directed to the defroster outlets; as in DEFROST mode. When vacuum is applied to the upper side of the vacuum actuator, the defroster valve is closed (full-up), blocking off the defroster outlets, and the heater valve is opened (full-up), allowing air to enter the floor outlets depending on the corresponding position of the mode valve; as in BI-LEVEL or LOWER modes.