When I first turn on the heat or anything, the controls hiss for a while them goes away. Why is this happening and is it fixxable?

In most cases, this is normal. The heater controls work using engine vacuum. What you're hearing is the bleed-off as you move the selector lever.

What does it mean if it doesn't go away? Meaning you hear a constant hiss...? Vacuum leak? {sigh} Probably...

Steve

It shouldn't hiss constantly. You can pull the controls to make sure the hose harness is still plugged in securely. It might be coming from one of the door control diaphrams too.

I dunno mine do it too. Sometimes I first fire the car up and they hiss until i wiggle them a bit. Then it goes away for a few days.

I can help you bro.

Take out your controls and on the back in a port with I think 5 vacuum lines going to it. That little port might be leaking, Did mine last year and its cheap ( like 12 bucks)

I'll get you the Factor-Air part # tomorrow.

Peace

Sweet, I appreciate it Keith - I guess that could be why I'm stuck with just a defrost mode; not enough vacuum to move it to the dash vents or foot well vents. I'd appreciate the part number if you can find it!

Steve

Ok its called a Rotary Select Valve
GM# 16022691 or 16032395
Factory-Air and Murray # is 36692

We stock it and it sells for $10.19

Hope this helps

Peace

Hey mine do that too... My other f body didnt do it though...


Kevin

mine dont hiss but its tuck on defrost too. how do i fix that?

Thanks Keith, I'll rip my dash apart this weekend and get one of them if that's the deal.

Thanks again,
Steve

finally , we habe a thread about this !
I need ot know which of the line son the control panel is the main feed from the engine, i have no vacuum at all on my Z28, its stuck on everything, vents defrosts, floor, everything, no vacuum hiss sounds at all , ever, its dead.... lol if I knew which hose feeds the panel then i could check at the carb/intake to see what happened, and also at the panel.

thanks

Mine does it too, has been since the vaccuum control thingie on my old heater control busted. I got another one from a car my buddy was parting out, and since then it has been hissing and hanging up on defrost. I think it's because the vaccuum lines were old and hardened and didn't seal to the 'newer' setup very well. I can get it too change though, if I go to a/c first for a few seconds and wait till it changes, then change to vent, then heat. Evidently the a/c has stronger vaccuum or a different setup for vaccuum than everything else. I'm going to try sealing the vaccuum lines better before I buy a new module.

mine does it to but only when i put on defrost

Oh man! That all makes sense! It feels like I may have a vacuum leak, and my heater controls hiss like a snake about to strike!!! Now, just to fix it! To those who has endevored on this - how difficult is it?

wish mine were hissing, I'll trade ya

Oh man - i dont suppose it's possible to remove controls w/o removing the panel under instraments is it? Damn, I woulda had it all taken care of today, too....

its simple to remove the that panel around the controls and radiom, justa few screws in a minute or two, and its off, easy, not putting mine back on til radio is in and controls have vacuum sounds like theyre supposed to...

good luck

hrrrrmmmmm - I have an obscured screw - which is why I was asking....

I replaced the entire control unit and moved parts around to get a good rotary control valve, BUT it is still stuck on defrost. What's up? Where does the engine vaccum come from. Recently redid the intake gaskets, maybe I forgot to hook something up. Help Please!!

Like I said before, I'm not so sure the vaccuum rotary selector is bad at all so much as I think the vaccuum lines themselves have hardened over time and no longer are pliable enough to properly seal. Maybe something as simple as a little bit of silicone or glue around the nipple on the rotary selector would cure the problem. That's what I'm going to try first, when I get around to it.