when i put my fan control on vent, all the air comes out of the defroster and not the vents, and you can hear a hissing noise at the vent/ac control. the a.c. works normally.

 

Sounds like a vacuum leak either under your dash or the vacuum line on your passenger side of the motor on top. Above the EGR crap. Should come straight out of the firewall between your heater box and engine.

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1992 Camaro Z-28 custom 25th anniversary, 5.7 TPI auto, 2.73 posi, t-tops, arctic white with 92' medium mettalic gray stripes with black border stripe.

1967 Pontiac Catalina 2 door fastback, 400 v-8, auto, cameo white, dark red interior

 

This problem is common. You might check the archives for more info.

JamesC

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