Thermal Vacuum Valve: Testing and Inspection

Fig.50 - EGR-PVS Opening Temperature Chart:

Switches With Two Connectors
1. Disconnect both vacuum hoses at switch. Connect a vacuum gauge to either connector on switch. Connect an external vacuum source at least 10 inches Hg or manifold vacuum to other connector on switch.

2. Start engine and allow coolant to exceed the calibration temperature of the switch as indicated in chart in Fig. 50, according to color code.

3. If there is no vacuum reading after coolant temperature exceeds the calibration point of the switch, the PVS switch is defective and should be replaced. If there is a vacuum reading, the switch is functioning properly.


Switches With Three Connectors
1. Disconnect EGR vacuum hose at carburetor and connect manifold vacuum or external vacuum source to hose.

2. Disconnect EGR vacuum hose at EGR valve and connect vacuum gauge to hose.

3. Start engine and allow coolant temperature to exceed calibration point of switch as indicated in chart in Fig. 50, according to color code.

4. There should be a vacuum reading at gauge after coolant temperature exceeds calibration point of switch. If not, the switch is defective and should be replaced.


Switches With Four Connectors
1. Disconnect vacuum hoses at PVS valve, then connect a vacuum gauge to either port marked D and M, and connect an external vacuum source to other port.

2. Start engine and allow coolant temperature to exceed calibration point of PVS valve as indicated in Fig. 50, according to color code.

3. If there is a vacuum reading after coolant temperature has exceeded calibration temperature of PVS valve, valve is defective and should be replaced. If there is no vacuum reading, that portion of valve is functioning properly.

4. Connect vacuum gauge to either bottom ports marked E and S and other port to vacuum supply.

5. There should be a vacuum reading at gauge with coolant temperature above the calibration point of the PVS valve. If not, the PVS valve is defective and should be replaced.