I had to shorten a bolt just a smidgen to get a neat job.

 

I did this and it fixed my problem. This really should be a sticky considering that you can't buy that part at any where. Napa and Advance both show it available online but if you try to buy it they can't get it.

 

Guys I'm so happy this helped! I thought this might help one other person. I glad it helped a few

 

Fantastic fix! I love it when you guys use these creative tricks to fix inherent flaws in our cars! Thnx!

 

Brilliant simply brilliant .....

 

Chalk up another victory for the hissing fix. pretty simple and easy to do. Recon this might fix my cruise control problem also? Probably not going to get that lucky but tgo is batting a 1000 for me. Great site Good people thanks guys.

 

I'm having the same problem with my temp selector. Even if the top selector is off, as soon as I slide the temp selector from all the cold it starts to hiss.

Did you find the problem? Was it a vacuum leak? We have been chasing these vacuum leaks down in mine for a few days now.... grrrr

 

Darn it...did the fix, but still have the hiss when I slide the temperature selector. No hiss on all the way cold, but begins hissing at you slide it hot. Must be a vacuum leak somewhere in the system. Anyone have any suggestions on how to isolate and fix it? When I take the little vacuum plug that has two lines into it that is on the drivers side off, not the main switch, and cover the holes, the hissing goes away.

I will say though, one little tab was broke and now the selector works great and each position blows strong...so I did think it fixed that for sure. Just be careful with those two (7) bolts that connect the switch underneath. Hard to get to and easy to break that plastic part that it goes into.

 

fire up the car with the HVAC control out of the pod. remove the pod for best access and track it like that.

 

Ok, tracked it down. Now this is going to sound really weird, but on the passenger side firewall where the vacuum line enters the car for the HVAC, there are two vacuum lines. One is for the the HVAC and the other is capped, it came like this from the factory. Maybe this was done so if there was a leak, the line could be swapped easy, maybe someone with more knowledge of the assembly of the cars can chime in why. there is one more vacuum line that goes through the drives side fire wall and that is for cruise control. Well, both my passenger side vacuum lines were hooked up to vacuum, we unhooked the one vacuum line and plugged it like it came from the factory, no more hissing from the temp selector and everything else works great. Hope this helps anyone else with the problem.

 

Just did this and it appears to have done the trick at least part of they way. Before all I had was air coming out the defrost vents. Now when on a/c or vent I have air coming out the proper vents and some out of the defrost. When on heat air comes out the heater vents and some out the defrost. When on defrost air only comes out the defrost. When it is off no air comes out anywhere.

I'm new to this car. Is this the way it is supposed to work? If not, could I have the vacuum switch clocked wrong or something?

Chris

 

Looks like you found the vac line for the heater core bypass valve, which would explain why it hissed when the temp was bumped up warmer; later cars had a secondary valve and vac line that opened to vacuum at warmer settings, and would open the bypass valve that's inline with the heater hoses on later cars. Had to track this one down on my old '91 bird awhile ago. I guess the TTA's didn't have one though? I never got to look around in one.

 

I'm no expert, but you may have another issue. Some guys have had the hissing from the temp selector. My hissing came from only 1 switch. I wish I could help, but I'm stumped.......sorry

 

Thanks for the reply jster1963. This is an example of how my luck goes when trying to fix things.

Let me add a little more detail. Once I got everything back together and started the car for the first time, air was coming out the vents and the defrost at the same time. So I thought ok, a little progress. Turned the car off and went inside. Came back out about 30 mins later to go for a little spin around the hood and when I started the car back up, air no longer was coming out the defrost. It was coming out of the vents only as I had the selector switch on vent. It is still working that way today. When I have the switch on heat, I get air out the heat vents and the defrost.

Also, I don't hear anymore hissing. My car is kind of loud so there may be some hissing that I can't hear. Before the fix, I could definitely hear the hissing.

I don't know if this makes it more unusal or if it helps get to the root cause of the problem. Maybe someone else will have experienced a similar problem and will have solved it.

 

Decided to take the switch out again and check everything out. Everything looked ok. This time I didn't tightened the bolt as much. Put it back in and now it seems to work perfect. I'm not sure if loosening the bolt was what caused it to start working, but it works for now.

On to the next thing!

 

Awesome idea. Thought I was screwed on this one. Glad to have such a cheap fix for once.

Thanks!

 

Yea just did this and it worked great. The only difference is I wish I would have used a 3/4" screw instead of 1/2". I ended up using a regular nut with red thread locker. If I used the self locking nut I had to tighten it too much for the threads to lock and would prevent the module from spinning.

I would have never figured out this hissing if it wasn't for you guys and this site. Chalk up another problem solved for TGO.

 

Awesome! I'm so glad it helped. The red locktite should be perfect. It's nice to know I'm not the only one still enjoying my TA;-)

 

Works great! Thanks for this.

 

Does anyone have the GM P/N for a 1992 Firebird for this piece we are fixing in this thread?

Mine is hissing all the time the heater is on too but rather than doing this to mine, I'd like to buy and NOS one from eBay or where ever and modify that one so mine is nice and clean and new.

 

I know this thread is super old, but I just did a modification similar to this and thought I would share, cost me $1.10 from ACE hardware. I got a 10-24 weld nut which looks like this

and a 10-24 pan head phillips head screw that was 1/2" long or so, 1/4 would be long enough, but they didn't have any so I just cut mine down. I also ground the head of the screw down some so it wasn't as tall, but not so much to remove the cross for a screw driver. The OD of the weld nut is ~1/4", so I drilled out the center of the vacuum valve, starting small and stepped up to the full 1/4". I inserted the weld nut on the side with the star tension washer and put the screw on the hose side. I put a little more grease between the rubber and the hose connector and assembled it all, checking the pre-load on the assembly as I went, guessed at where it should be and added a little wicking thread lock to the inside of the weld nut

Doing it this way made the whole thing really short/compact and doesn't interfere with anything

If you want to buy weld nuts online from McMaster Carr the part number is 90596A114 and the screw is 90272A238 but you have to order each of them in packs of 100.




The scratches on the weld nut are from me cutting the extra length of the screw off.

 

That looks great! I love that we can engineer something that needs to be fixed and make it work. I drive my car every week (except when snow/salt is on the roads) and it still works. Thanks......

 

Necessity is the mother of invention?

I remember reading your thread way back when, but I couldn't find it before I went to the store, so I just had to improvise when I get there. This was super cheap and low profile, so I went with it.

 

Just did this fix this weekend on my '92. Now my controls work great without any hissing. Car seems to idle a little better as well. Whole project was made a lot easier with the radio removed first.

 

Lon, at TopDownSolutions has them if you don't want to do the repair.

 

Which will likely be a used piece and be 20+ years old at this point. Unless Lon started getting them made

 

"Refurbished", so yeah its used but its still available and some people try to keep their cars completely original (not me as evidenced by my GTA).

http://www.top-downsolutions.com/ind...product_id=289

 

Old thread but good info, ill probably do this tomorrow. I was driving a few weeks ago, and moved from max to vent, and all it did was hiss and not make the change.
I thought most companies had gone away from vacuum AC controls but apparently Ford and a few others still do it on their new cars.

 

I just did this to my car as well; works great!

 

Thats what i did

 

This thread totally saved my ***. Major props! Thought I'd add to the thread. When I was repairing my HVAC switch using this method I dropped it and broke off the nub that communicates with the switch on the dash
I first tried to epoxy it together but that didn't last so I instead threaded a cut off screw through the plastic- and it works! Hope this might help someone else down the line.

 

Old thread but good thing I found it. That hissing noise is driving me nuts like there is a snake under my dash that refuses to leave. Watched the video on you tube last night and it was very helpful. Just have to be careful and not over tighten the bolt.


GM knew this part was going to be a problem and they discontinued it. Typical knowing they could have improved upon it and made an updated part for pennies on their end.

 

Did the fix today and worked great. It no longer hisses like crazy and each selection of a function is faster.

The only thing that was a bit of a bother but has to be followed, is getting the pressure between both pieces just right for it not to let out vacuum and turn without too much force. I left it a hair more firm but still can select with a single finger.

I personally didn't use the washer as it didn't seem to need it but down the road we'll see.

Btw, the original center clip that help everything together was not broken yet failed anyway by not producing enough force to hold bold pieces together.

 

I saw this a while back and did it myself. it made a world of difference.

 

Now let me ask you this. Does it still hiss only when you switch from setting to setting?

 

Ok, I got around to the fix today. I bought the 8-32 x 1/2 screw, washer and nylon locknut at a cost of thirty-three cents from Ace, and in less than an hour I was up and running. I was surprised that the two retaining clips were in place and unbroken. I repaired the selector in my car, which is black. Recently I yanked another from a bone yard. It too was black. But note the white one. Any difference except color?

JamesC

 

Those 2 clips are not the ones that caused the hiss on mine. It's the one in the center that holds the 2 parts of the switch together. I don't think the color matters, but I'm not 100% sure. Good luck and thank you very much...….

 

Which has two clips/fingers.

JamesC