Vacuum Leak? 1999 Jimmy SLT

Marie L
10-18-2011, 08:13 PM
Need help to diagnose possible vacuum leak. Experiencing hissing noise and have targeted noise to be coming from under dash. If I turn the control dial from defrost to floor or vent sometimes the leak stops. Air leak also stops eventually but is becoming more prominent over time. Any thoughts?

10-19-2011, 08:10 AM
You need to trace the hoses that go in thru the fire wall, maybe a vacuum operated mode door in the hvac system.

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