The rotary switch on the back of the HVAC control panel....my son's '92 RS has a BAD vacuum leak at that switch(hisses like a damned cat).

the clear rubber/silicone plug is in good shape, and the plastic lines are free of cracks/tears....the amount of "leak" seems to change as i move the slider from A/C to Vent and such. I pressed on the switch itself, seemed to get quieter as pressure was applied.....of course it went back to what it was when I stopped.

Does GM offer this switch as a replacement part, or is this a non-serviceable item?

I "believe" this is what you need: Valve Vac Sel GM part # 16032395. The number is good on GMPartsDirect.

JamesC

Just replaced that on my RS. My a/c was going to the default mode of venting through the defrosters, and it was hissing bad,replaced that part and I am good to go.

Mine does the hissing as well but not the venting only through the defrost area yet and the hvac mode slider also "catches" around the center of the movement and makes a click sound when pushing past it. If I come at heater mode from one direction instead of the other I can make it stop hissing. Do you think this valve replacement is my problem too?

There is a good chance it is the same problem especially if it has not ever been replaced. I would say it is on it's way out. Point is, it is probably falling off the mount it is on and that is why your control lever is hanging up.

I was able to get the AC Delco piece through Rockauto recently and there are discount codes posted here somewhere by the above JamesC. Once you have it out you can check the integrity of each of the vacuum lines connected to it with a MityVac/brake bleeder, which you can 'rent' at AZ or one of the others.

You can also get a discount code from internet sites, just type in RockAuto discount codes, it will at least get you 5% off, I do it everytime I order from them.

I also have that "hissing" sound sometimes when going to HTR or the "window-mode" to the right. Sometimes its making that "PSSSSSSSSSSSSSSSSSS" sound for like 30secs and then stops.

All other positions is quite, and when I put it from OFF - MAX - NORM etc I hear the AC engage and so..

Could it be that part (16032395) you said thats making the "PSSS" sound in HTR/window mode ?

Yes it could it has a gasket between the two halves that wears out.

Thanks I will order one of these to have in the garage, I will look into it this winter when snow falls and the car goes to sleep for the winter..

Before I started ordering parts I would check the lines too I just said it was possibilty.