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Vacuum Switch Valve

Remove Vacuum Switch Valve (VSV) from vehicle. Apply vacuum to the diaphragm nipple. Blow through either port "A" or "B". See Fig 1 .
VSV should be closed when vacuum is below 2.6 in. Hg and open when vacuum is above 4.2 in. Hg. If the VSV does not function, replace valve.

Fig 1: Testing Vacuum Switch Valve

Courtesy of FORD MOTOR CO.