1999 Suburban Vacuum Noise in dash

[mclan]

1999 GMC Suburban with anoying vacuum noise in dash. Unaffected by fan heater speed. Just started few hundred miles ago. Fairly sure it's vacuum related. Goes away while under load, comes back when load is gone.
If I had to guess, heater/AC control related.

Any vacuum controls in dash?
Any hints on removing dash, access to these controls?

Any help would be greatly appreciated.

Thanks

[moisture1]

Hi I know it is almost 4 years since you posted you question If you happen to get this message and have had luck finding out what your problem was i was hoping for some info as I am having the same problem with a vacuum leak type sound coming form the dash.

Thank you

[540 Olds]

Hello,

I have the same problem....same noise as described; when I shut the engine off, the noise slowly dies with RPM. Noisier inside the car than outside. When I look under the hood, I can barely hear it, but it is annoying inside.

Anyone have any luck with this, please let us know.

Bob

[jdmccright]

I would normally remind new users to refrain from reviving old posts, but since this thread didn't have any resolution, call it a friendly request for the future.

The vent selector door is moved using the engine's intake vacuum. There is a vacuum-operated actuator with a rubber diaphragm inside that pushes/pulls the door to the correct position. The diaphragm has probably developed a hole, thus giving you the hissing sound. The sound may change when you move the selector knob, but doesn't cease.

I do not know the procedure for replacing this...I've done it on a '96 Jimmy and was somewhat easy thanks to whoever in GM brilliantly thought of allowing the dash to be pivoted back away from the cowling. Don't know how the Sub is setup, but it's likely accessible only from underneath or by moving/removing the dash. The part itself is fairly cheap, but you pay for it in scraped knuckles and hand cramps from all the sadistical contortions needed to reach in there. But it can be done.

[540 Olds]

Hello JD,

I got a phone call from RSmith about this problem. He had same thing and tracked it down to his fuel pressure regulator. He had same vehicle; '99Sub, 350 gas, 1500. He explained his noise and it's identical to mine in that it changes tone/volume as throttle is moved, and dies out with engine rpm when engine is turned off.

I will check one more thing, then go with a new regulator.

Thanks for the reply on this. It was my first time on here for a while, so I just "paged" my way through until I found someone having the same problem/noise as I was.

Bob