jster1963

If the cause of your hissing HVAC is the selector switch, I have a permanent fix. You need a 8-32x 1/2 screw a washer and a nylon lock nut.

I have replace this switch 3 times in 3 years. I took the switch apart and found the cause. The spring or the plastic fastener fails.

If you remove the fastener and use the screw and nylon nut to hold everything together, you will be in business. I posted a youtube vid if you want to see how it goes together.
http://www.youtube.com/watch?v=Mv782CIJDks

micktroup2

This is what I love about this site- folks who really care, finding fixes for the design flaws in our cars! The greasable bushings for the door hinges, the door rattle fix thread, subframe connectors, THE LSX SWAP, now this... let's keep it up and keep these things on the road! Great repair and simple video!! Well done! I saw someone suggesting disassembling the switch and soaking that rubber seal in brake fluid(!) but it just didn't sound right... when you hear hoofbeats, think horses, not zebras and your video showed the obvious culprit. I am going to try this as soon as I get home!

GerryCat09

iTrader: (1)

Awesome, the hissing has been on my nerves for a while, and I have never gotten around to investigating a solution. I already have all that hardware in my garage, so I'm going to give this a shot.

jster1963

Micktroup2-Thank you very much for the kind words! Please let me know if this works for you. Thanks again.....

GerryCat09-If your hissing is from a broken switch, this should fix it. Please let me know........Thx!

ps. My car is so quiet now;-)

JamesC

iTrader: (5)

Most excellent.

JamesC

Tuned Performance

iTrader: (92)

Im kinda fond of hearing the sound of angry snakes hiding in the dash.

micktroup2

Well, I took mine apart, BREAKING THE SWITCH IN THE PROCESS- DAMN!- before I check it, LIKE AN IDIOT.
Anyway mine was not the problem. Mine hisses when I slide the TEMPERATURE lever- the bottom one. I too keeps old parts, like all of us I would venture to guess, and had the other switch.
I swapped it in and the damn thing still hisses if I slide the lever away from cold, so my problem must lie somewhere in that.vacuum line.
Anyone got any ideas?

Great idea for a fix, though, if that is the source of your problem...

jster1963

I'm sorry! Mine has always been the top selector switch. I would try plugging the vac line with my thumb or something and see if it still hisses. If it does, it must be in the line. If it stops, it must be the switch. I sure hope you get it fixed!

izzy77

sweetness! ive been at it a day trying to stop my ac hiss(just got the ac retro-ed in my 92 rs) i figured id give the ol search on thirdgen a try......awesome!

jster1963

No worries! Good luck and please let me know if it works......

QUICKCHICKEN

iTrader: (12)

i posted the link to my local club site in our archive forum. thanx much.

kman71

Great post.

I have a couple issues with mine. I think I have a vacuum leak somewhere and wondering if it could be this switch. I don't hear any hissing, but the top selector works but does not change where the air goes, it seems it is defaulted to the defrost vents only. I have it apart but can't figure out how to get the switch off the heater control panel. All the wiring seems pretty tight and I can't pull the heater control out very far to get a real good look at it and figure out how to get the switch out.

Any advice on how what the problem could be and how to get the switch out to do the repair?

Thanks.

jster1963

Thank you very much! The system is designed to default to defrost when there is a leak (fail safe). It could be your switch or a leak somewhere else. I could always hear mine hissing as I tried to select something different.

If you want to remove the selector switch, there are 2 places that it connects. The vacuum hose assembly has a "one way" crimp washer. Be careful pulling it off. I had to twist with needle nose pliers and pull at the same time. It is easy to break off the plastic tip. And YES! It is very tight pulling the panel out, so be careful.

There is also a small screw on the bottom. I can't remember if it is a phillips or a 6-7mm head. Once you remove the hose and the screw, it just pulls out. You can always try the switch and if it doesn't work, keep on trouble shooting.

My issue has always been the switch, so I can't help very much if that is not the problem. Good luck..........

80schild

iTrader: (5)

Mine seems sluggish. For example, if I want to go from DEF to NORM, I have to go to MAX first, let it get started out the front vents, then go to NORM (hearing the hissing during the whole process).

Its the same thing if I want to go from HTR to VENT, seems I have to go to MAX first to get it started.

jster1963

That sounds like how mine started. Then after a while it only hissed and stayed on defrost. That selector switch is fairly cheap. I'd try it and see what happens.

JamesC

iTrader: (5)

Pics/info in the following link may be helpful:

https://www.thirdgen.org/forums/elec...ml#post5278772

JamesC

norcalz28

iTrader: (13)

Looking forward to trying this, and not having to use VENT all the time. Thanks

Will

TheGr8erG00d

iTrader: (2)

Decided to give this a shot. It would have worked from what I could tell! Unfortunately, as I took it apart, I dropped the spring and lost it. I scrounged around for an hour trying to find where it had fallen to.

80schild

iTrader: (5)

I did this today, and it worked! I still hear just a slight hiss, but everything now works like its supposed to. It changes from one function to another very quickly now. Now i just need to fix my compressor.

Thought I'd mention too that my plastic piece was not broken like the one in the video, in fact it still seemed pretty tight to me, but it apparently was just loose enough to cause problems. I do think maybe that rubber piece gets worn down after awhile, which means it needs to pressed tighter for a seal.

chevydrvr

iTrader: (1)

I just did this a few minutes ago...worked great! Any hiss I hear is no more than any new car with the same type of system. Awesome job!

jster1963

THANK YOU very much! I'm glad it helped.......

80schild

iTrader: (5)

This may be just a coincidence, but it seems like my car idles a little better since I fixed this. Could this thing have caused THAT much of a vacuum leak?

jster1963

My first one didn't have a broken tab either. It just got loose like yours. I guess it gets too loose to work. And yes, a vac leak could have caused an idle prob! It's so nice to select heat or a/c and get it;-)

rwstegne

Thanks man!!! I appreciate you taking the time to share and document how to fix this. I just fixed it and it was a easy thanks to you.

Now, does anyone know how to trouble shoot the blower motor switch? Low and the two medium speeds work, but high speed does not. All ready tried a new motor and that did not fix it.

JamesC

iTrader: (5)

A relay controls high speed. Check the following link for useful info:

https://www.thirdgen.org/forums/elec...aro-rs-no.html

JamesC

jster1963

rwstegne: Thank you! And, you're welcome! I'm glad it helped. I see JamesC answered the hi speed question. I'm glad he answered, cuz I had no clue;-)

Thanks JamesC..........

TheGr8erG00d

iTrader: (2)

This is a great fix. I still get a small amount of hiss, but it's next to nothing compared to what I used to have and now I have full functionality of my controls. Be sure not to make it too tight as it can bind and potentially break something if it is too difficult to move. Just tighten it a little at a time.

Thanks again for this great fix. It's great to be able to run AC, vents, etc at full blast again.

kmcn47

sticky this someone

ZF6camaroZZ4

So the nut clears the switch housing on the TA's?

I ran a large sheet metal screw down the center of mine(down the nut side on your picture). I had to grind the head pretty flat for the vacuum switch to mount back up.

jster1963

Yes. It fits perfect. I'm not sure if you looked at the youtube vid (there is a link), I put it back in just like in the vid. I'm not sure about the Camaro. Good luck.......

kmcn47

camaro works fine too good job

jster1963

Thank you very much!

cmk-2

iTrader: (1)

Great information. Thanks, I have been living with the "hiss" for 3 years now. Thanks to you it's gone. I also found that the two nuts that hold the vac lines on to the selector were missing. Replaced them and the cold start problem I had disapeared also well. I guess the vac leak can cause more problems then just a Hiss.
Robin 1987 5.7 60,000 miles

jster1963

Thanks you so much! I'm glad it worked. I don't listen to the radio much, so the hissing was driving me crazy! I didn't know a vac leak could cause other problems either. Thanks again......1987 5.0 125,000 miles on mine and I'm the original owner (yes I'm old) LOL

cmk-2

iTrader: (1)

Original owner..How Cool. I had an 1987 in 1987 and wanted the exact one again. Did a VIN look about 6 years ago and up spoke with the current owner. "Yea I got it..It's on blocks out back" I asked if it was covered "no.what do you want to give for it?" So I started looking for a exact copy in good shape.

jster1963

Thanks. And Wow! That's really cool! I hope someday you'll get your original VIN and not have to give an arm and leg. In the mean time, love the one you're with;-)

munk20

iTrader: (1)

great tip, need to do this myself

jster1963

Thank you very much!

policeintercept

well for start thanks to jster for the cheap fix. lol. cost me 33 cents. no more hissing. however. still only blowing threw defrost. i pulled the vac lines from the back of the unit and still no hissing.... wont switch to other vents. any ideas? it worked 3 days ago

jster1963

You're welcome. As far as still being on defrost, I'm not sure. If you pulled the lines off in the back and you start the car and there is no hissing, something is wrong. It is a vac leak. It should hiss like a snake, so I would start looking for a vac leak. Good luck.......

SaxophoMan

It works! I never would have guessed this since my clip that held in the washer wasn't broken and it even seemed pretty tight. I accidently broke it during removal. Or maybe it broke because one of the hooks was weak. I'll never know.
After performing your fix, it would still hiss each time I used the selector, but only for a second or two and then it stopped completely.
My only worry is that when the ignition is on (and car is off), it still only blows out the defroster. But before that, when the car was running, it operated normal. Hopefully it's just the default for when only the ignition is on and I don't have to fix something else.
Another note, I couldn't remove the control switch. I had to remove the radio underneath to have any room. Once the radio was removed, I had enough access to the selector, so I just removed that instead of the whole controller.
Thanks for the help!!

jster1963

You're welcome! I'm glad it worked. I'm not sure why the defrost is doing that. It is normal to hiss for a few secs when you select something new. I've bought this car brand spankin' new in 1986 and it did that from the beginning. Good luck and I hope you don't have to fix anything else.....

SaxophoMan

When it's running, it operates normally so I'm not sure either. Glad it works though, I never would have guessed this fix.

Scoundrel

This worked amazingly well on my 87 camaro. Thank you so much!

85firebird89gta

This is helpful. I spent a lot of time searching for this control and then when I found it and bought it on Amazon I ended up with someone elses bad part put in an old box that they resold to me. I then found one, via internet, all the way at a place in Australia and had it shipped to me. That one worked. But, to be able to fix this permanently when it happens again is terrific.

Some of these parts are really hard to find. The other one that drove me crazy was the headlight isolation relay for my 85 firebird. It took me months to find one in working condition and I bought a couple of junk ones from people before I got one that actually worked. Maybe you can come up with a relay fix too.

nuggie

really that simple? Is this the same set up as the 4th gen?

jster1963

Mine was that simple! I have no clue about 4th gen, sorry. Good luck.....

W.E.G.

Just did this repair on my 88 SC.

Solved the "stumbling" problem I was having in third gear during light throttle.
Also noticed a BIG difference in low-end response in other gears.

The toolz:


Notice how the "hub" that is supposed to hold the parts of the valve together is just flopping loose.
Both locking-tabs were broken.
Once I removed the valve from the heater control unit, the various parts of it just fell apart from one another.


The little black piece (a.ka. "center-hub")on the right is the part with the broken (absent) locking tabs.
The star-spring is what keeps tension on the two halves of the adjustement mechanism, and is what keeps you from having vacuum leaks until the center-hub fails.


Pic of the two "halves" of the valve.
The part on the left is the part that plugs into the vacuum harness.


Here is the part that plugs into the vacuum harness.
Its not possible to plug it into the vacuum harness upside down, but you do need to pay attention when you re-attach it to the control-lever assembly.
You have to orient the assembled valve so that the "nub" that engages the adjustment-lever on the panel is "on top."
There are two metal spring-clips that engage the outer arms on the part.
Be especially careful when removing this part from the vacuum harness.
You don't want to break the arms. I put grease on them to make the spring-clips slide more easily during disassembly.

W.E.G.

Here is the "nub" that engages the levers on the control panel.


...and another pic of the "nub" on the repaired part.
You will notice too, at about 1 o'clock in the pic, is a smaller nub-looking thing. That is the index-nub for the rubbery disk that is sandwiched between the two "halves" of the valve assembly.


The repaired part attaches to the vacuum harness by just plugging it into the harness.
The two black-metal spring-clips hold the part onto the vacuum harness.
Once the part is attached to the vacuum-harness, two black metal screws hold the part onto the control panel assembly.

.
.
.

W.E.G.

Here is the labyrinthine inner-sanctum of "the thing that hisses."

I hissed a bit myself when I saw all the cat hair and assorted smegma that this thing had inhaled over the years.


Here it is, after a thorough disinfecting, and application of a coat of Wal-Mart silicone spray.


You want it to be smooth, clean, and slippery when it engages this part that leads to all the vacuum solenoids.


Here is the multi-colored vacuum harness where it all plugs in.
Pic shows back-half of valve still attached to harness - which is what happens after you remove the two black-metal spring-clips, and when that center-hub has already given up the ghost.
See upper-center area of pic.
(stereo harness in lower left-hand corner of pic)