syc0path

We had some 80* weather a couple weeks ago (and last week we got 6" of snow -- welcome to Michigan ). Anyway, when I tried to use my vent or AC, the air came out of the defroster vents on top of the dash.

I checked for vaccuum leaks and I can hear a leak coming from the heater control in the dash. I took the radio and heater control out and tried to find the leak so I could seal it. But I couldn't seem to narrow it down. I could make the leak worse by squeezing the disc that rotates as u select AC, vent, heater, etc.

Here's a pic... does anybody know which color vaccuum line controls the vent setting? Anybody else have this problem or have any suggestions?

Infinitro

I am going to assume you have a loud hiss as you go to slide the lever over to "HOT". Look under controls and see if you have the little vacuum switching valve on the bottom left side. It is moved by the hot\cold lever,if it still has it's locating pin to hold it in the little slide that turns it to contol vauum to the heater valve and all that works smoothly I would guess since you have air from unwanted areas that you swap the hoses under the hood that actuate the heater valve and the vacuum source. IE: tube hooked to vacuum at manifold and goes inside to the heater controls gets pulled and put on heater valve.Hose that is presently hooked to heater valve gets connected to vacuum source at the engine. Seen this alot they get swapped when working under the hood.

Infinitro

Obviously the word in the above text is vacuum. The valve I am referring to is the one on the left in the photo with just the 2 vacuum lines going to it. You have to look underneath to see if it is operating.

JamesC

iTrader: (5)

I once had a similiar problem, which was repaired by replacing the piece that accomodates the multiple vac lines and which switches sources.

JamesC

syc0path

No, that's not what it's doing. I only hear the hiss when I'm on vent or AC... changing the temp slider doesn't have any effect on it. And the hiss isn't that loud -- I had to listen very closely while idling in the driveway w/ the radio off before I could hear it.

I should also mention that the vent works sometimes -- it seems like the hotter it is outside, the more likely the cool air is to come out the defroster vent.

Yeah, that makes sense, becuz I couldn't seem to find the leak just by playing w/ the hoses. So maybe it's something internal to the heater control itself. Hmm... so where am I gonna find another one of those??

JamesC

iTrader: (5)

I had one at hand from a used control head, but IIRC, the part was still available from GM.

JamesC

thunderstick

the piece that accomodates the multiple vac lines is your problem. over time it gets dry and won't hold a seal worth a crap. reason the air you have comes out the defrost only is cuz that is default. if nothing else works, that will. anyways, you can replace that piece (i thought it came as an assy with all the vac lines attached cuz that's how i bought it) or another trick i've heard is that if you disconnect that from that vac select switch thingy, take a q-tip and apply vaseline to the inside of each of those vacuum line. apparently that has a softening effect on it and will rejuvenate it a little bit. how long it will last is beyond me cuz that isn't how i fixed mine, not to say that trick doesn't work. i never tried it, just heard of it. a little more advice would be that if and when you pop that connector thingy off the back of that switch, those little captive washers might get dropped, so i'd put you a rag or something in there first... good luck with it.

KAM

JamesC

iTrader: (5)

Tried the Vaseline business--don't bother. Replace.

JamesC

thunderstick

jamesc, do they sell just that piece alone that attaches to the back of that thing? i was just wondering cuz what i bought came as an assy with the vac tubes attached to it like a harness type of thing. i ended up just clipping that "connector" thing off and attaching the tubes individually and securing with zip-ties. it works for now, but until i open that dash up to fix a couple of other things, i'm gonna leave it as such...

KAM

JamesC

iTrader: (5)

Since I took mine from the HVAC controls of a used piece, I can't say how a new piece would come--IIRC, the new piece was only a few dollars though. I simply slipped the vac harness off the old piece and reinstalled it on the replacement piece. Easy swap.

JamesC

coolcamaroZ28

I had this exact problem when I got my 91Z about a year ago. I also had no cruise control, which also runs off the vacuum. The problem at least for my car (which was also 'hissing' at the HVAC controls) was a broken vacuum line under the hood, where it exits the manifold. Check under your hood, there should be a little sticker showing the schematic of the vacuum lines. If you haven't already checked this out, there is a good possibility that it can just be a worn or broken vacuum line. I replaced the line that goes from the junction valve near the manifold (where it splits between the cruise if you have it and the HVAC controls) all the way up to the cruise control module and everything now works. I would also check the line in the system that runs to the 'ball' (recovery or overflow tank?) under the fender to see if it is intact... --John

syc0path

Yeah, that's a good tip -- I should have mentioned that I checked under the hood first and didn't see anything. I also checked my cruise control -- it engages properly, maintains the correct speed, etc. So I'm pretty confident it's something in the dash.

Does anybody know the part # for the heater contol assembly in the dash so I can order it?

Claimchaser

Tell me more about the situation you have described for me.I have a recent purchase camaro and it doesn't switch off of defrost but the temp and fan speeds work fine.I found a small black plastic vac line coming from the harness under the hood beside the heater/AC housing and connected it to a vacuum and now it hisses loudly at the controls unless it is on full cold but still does not change from defrost.

JamesC

iTrader: (5)

Defrost is the default setting. If you hear a hiss at the control head, you no doubt have a vac leak. Valve Vac Sel GM part # 16032395.

JamesC

Claimchaser

It's not the control head thats leaking it's the selector valve on the temp side not the control side.It's discontinued.

JamesC

iTrader: (5)

I "believe" we're discussing the same part:

https://www.thirdgen.org/forums/atta...duct010707.jpg

If so, the part number above is good at the following site:

http://www.gmpartsdirect.com/index.c...TOKEN=43475709

JamesC

Claimchaser

Nope that is not the part I am talking about.I need the valve on the other side that has two hoses going to it.It is hissing when not in the cold position.I wanted more infomation on the under the hood vacuum line locations.I have found one black plastic vacuum line and I plugged into a vacuum at the manifold and not it just hisses when off of cold.Now it was mentioned prior that there were two vacuuum lines unde the hood for the HVAC? I need to locate these and make sure I have it connected correctly before I buy any parts.It doesn't adjust from defrost but I read prior that this is a default setting if it is leaking from anywhere? So thios doesn't tell me that the control valve is bad.it doesn't hiss with a vacuum leak.not sure it is even getting a vacuum.Hope this helps.I was told by my local dealer that it was discontinued,The other part is a vailable at the dealer for $31.00