2005 Pontiac Montana Hissing from dashboard

2005 PONTIAC MONTANA
181,500 MILES • 6 CYL • FWD • AUTOMATIC
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SEAWAYGUY
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When I switch from my defroster to my air conditioning, the air conditioning does not work and there is a "hissing" noise coming from the dash/vent area. I am assuming that this is a vacuum line issue. Would my problem be in the passenger compartment behind the dash or elsewhere on the vehicle. Prior to this the a/c was working fine. After sitting for 2 weeks, the next time I used the vehicle, this problem was present.
May 27, 2010 at 7:07 PM
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MHPAUTOS
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Hi there,

This is defiantly a vacuum leak, it will be up under the dash i would be looking around the main feed into the control unit, i don't know a lot about these cars as i am in Australia, so if we get a bit stuck i will pass this on for you, start looking under the dash around the heater control unit.

mark (mhpautos)
May 27, 2010 at 7:32 PM