Hi, I have an annoying problem right now.
I can get hot or cold air, but not matter where I set the air switch, it stays on the vent that blows on the window.

Anybody have some pointers on what to look for?

thanks

 

A loose or damaged vacuum line that controls the damper position in the air duct. Do you hear any air noise when you more the selector lever from OFF to AC to Heat to Vent to Defrost?

 

This is when a hand held vacume pump is worth its weight in gold. The defrost is the default position. You need to check the vacume line coming in to the interior. It's a hard black line that comes off the intake around the distributor and enters through the fire wall. I used my vacume pump with a plug in the other end to see if it held vacume. If that checks out, remove the HVAC controls and on the back side you will see a group of small colored hoses. These are connected to the vacume actuators that move the door flaps in the dash to direct the air. Again I used the vacume pump to test each colored line with the blower running to see if the actuators worked.

In my case, all of the vacume lines were fine and all the actuators worked. The problem was vacume selector on the HVAC control. It's the white plastic piece were all the colored vacume lines attach. One piece is stationary and the other half rotates when the selector is moved, thus directing the vacume to the correct actuator. In between the two halves of the selector is a rubber gasket that looks like maze. This rubber gasket gets dirty, dried out, worn from rotating etc. causing a vacume leak. I cleaned mine up and applied a thin layer if silicone grease and it started working again.

If I had to guess, your selector is doing the same thing. Check it out, just note the position of the parts before taking it apart.

 

Stick an ear to the HVAC. You may be able to hear the leak. Should the selector be the culprit, the following is what you need: Valve Vac Sel GM part # 16032395. The number is good on GMPartsDirect.

JamesC

 

I was wondering if a replacement part was available. I just had not had a chance to check my parts manual. Thanks!

 

I'm in the same boat as you. Now I have to check all the things mentioned above and see what I can do myself

 

Like I said the hand held squeeze type vacume pump is worth it's weight in gold for this. You can get cheap one at the parts store that will work just fine. It's a good tool to have anyway, makes brake bleeding a 1 min. job.

 

I had this problem last month, I got it fixed though. I have an extra switch if you have trouble finding one

 

On my 91RS there is a fitting located between the throttle body and the distributor,it has a 1/4" nipple on it.In between a flexible rubber hose that attaches to the nipple and a hard plastic vacum line that goes through the firewall,there is a plastic union which has three nipples,one goes to the fitting that mounts to the manifold,the other to the hard plastic line that goes through the firewall,and another which I have no idea what attaches to it.This union is broken in two and I believe it is the culprit responsibe for my a/c or heater not blowing through the adjustable vents and only through the defrost vent near the windshield.My question(s) to you guys is what is the name of this "union",and what attaches to the third nipple on this union,also where can I find this part? Knowing its name would be a big help.Thanx ,Jving.

 

Not quite sure what it is called, but it's prob. just a union to provide vacume to the HVAC and the other prob. goes to the cruise control or something. If you go to the parts store they have a selection of vacume fittings. I have seen them at autozone because I noticed they had the hard black vacume line that goes through the fire wall. Let us know how it goes.

 

That union is really a check valve that allows vacum to be drawn into the engine and not let it out,I never did locate this part new anywhere,Instead I got it off a 93 firebird.As soon as I installed it all my vent positions worked.

 

Do you think you could post a picture of where it is?
That would be really helpful

 

So I looked at the selector and removed the fitting with the little hoses.
With the engine running there is no suction from any of the hoses.

I am guessing thats the problem, does anyone know which hose on the inside should have the vacuum?

 

I once had a door flap that was stuck in mid position because a pencil was dropped down the defroster vent on top of the dash. I saw the little brat do it. I didn't worry about it till the winter when my heater was barely working then I remembered about the pencil. That was about 2 hours of cussing tearing my dash apart.

 

well I fixed it. Apparently the previous owner decided to unplug the vacuum hose where it goes into the firewall :P