Thermal Vacuum Valve: Testing and Inspection

Fig. 3 Lambda-sond (oxygen sensor) system vacuum hose routing:

In order to test this valve, coolant temperature must be below 131°F.
1. Disconnect hose from pressure differential switch, Fig. 3, and blow into hose. There should be a connection between pressure differential switch and intake manifold.
2. With temperature above 131°F, the thermal vacuum valve should close off the connection between the pressure differential switch and the intake manifold and connect the switch to the temperature controlled ignition advance solenoid.