noise from under the dash on my 1999 jimmy

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I need to track this noise down, it sounds like a door trying to close. what causes this, vacum checked out ok. I have airflow to all areas, but i did have to unhook the heater hoses, heat would not shut off, which told me the doors were not closing propely, but I do not know how to get the dash out, to replace the door... please help.............it is a 1999 jimmy slt 4x4, 3.1 engine.it has automatic heater controls, and it does have a/c that blows cold. just had a new compressor put on.the noise sounds like door trying to shut, so i believe its vacum.its coming from the front of the heater box, you can see the door trying to shut but it only goes half way, but I can get into it to see what I need to do. Thanks... I hope this helps , Lord knows I need it.
Thanks,Bush:banghead:

Sounds like there is a hole in one of the vacuum actuators for the doors. Remove all the lower dash trim pieces, drop the steering column, and then remove the screws that run along the top of the dash near the windshield (some are under the speaker grille guards). The dash should rotate back towards the seats on two hooks on either side of the assembly, allowing access to the ductwork from above. Hope this helps!