See Figure 1
The vacuum control valve is provided to reduce the engine lubricating oil consumption when the intake manifold vacuum increases to a very high level during deceleration. The vacuum control valve senses the manifold vacuum. As the manifold vacuum increases beyond the specified valve, the valve opens and air is sucked into the intake manifold. Refer to the illustrations.
Aside from a routine check of the hoses and their connections, no service or adjustments should ever be necessary on this system.