Vacuum Switch: Description and Operation

Fig. 22 Typical vacuum switching valve:

The Vacuum Switching Valve, Fig. 22, has 3-way ports, two of which are operated by an electrically controlled solenoid plunger which is energized when the coolant temperature is below 122 degrees F or for 10 seconds after the Wide Open Throttle (WOT) switch is energized with the coolant temperature above 122 degrees F.
The solenoid plunger is de-energized immediately after the WOT switch is turned off during this 10 second period.
When energized, the Vacuum Switching Valve connects diaphragm chamber ``B'' of the air switching valve to intake manifold, allowing application of manifold vacuum. When the solenoid plunger is de-energized, the Vacuum Switching Valve ports are closed, thereby diaphragm chamber ``A'' is connected to diaphragm chamber ``B''.