Vacuum System

All mode valves except the temperature valve are controlled by the engine vacuum stored in the vacuum tank in the engine compartment. The vacuum is routed by a vacuum switch in the control assembly to any of the spring-loaded two or three-position vacuum actuators. One vacuum actuator is linked to each air valve.

The vacuum switch in the control assembly is controlled by the mode control knob. For each mode knob position, the vacuum switch directs engine vacuum to specific hoses and vents the remaining hoses to normal air pressure. When a hose vents to normal air pressure, the vacuum actuator's internal spring expands and holds the associated air valve in one position. When the vacuum is routed to the hose, the force of the vacuum overcomes the internal spring pressure and moves the air valve to the opposite extreme of its travel. In this way, the mode control knob positions the mode valves for the selected operating mode.