GettnBetter

I have a 2000 convertable.

Just recently the AC began making this hissing noise, as if a vacuum actuator of some sort has a bad seal.

If I turn on the AC I don't hear the leak but if I turn it off I can hear it.

It sounds like it's coming from behind the cockpit temperature thermister but I could be hearing reflections.

If I start the car cold with the AC off I don't notice the hiss until I turn the AC on and back off.

Before I tore into the dash I thought I'd ask a few questions.

Is this a common problem?

Anyone have any ideas what I should be looking for?

Bill Curlee

Unless its a constant HISS, or some HVAC mode doesn't work correctly...it sounds completely normal. Your HVAC "DAMPERS" all work on engine vacuum to reposition each damper mode.





Some of the dampers have a modulator that applies vacuum to one side or the other to change modes. When you change modes, you vent off the vacuum to the side and apply vacuum to the other. The venting results in a hiss noise from the muffler in the picture:





See if you can pin point the venting to the drivers side dash.

BC

GettnBetter

Excellent pics! Thanks for that.

That component has to be where the noise is coming from. It just started recently. I figured it was engine vacuum. Maybe a hose has come loose or one of those actuators seals has failed. I never heard the noise in the past.

I'll dig deeper into the dash and see if I can locate the exact point of the noise.

BELVIN20

Just had the same problem with my 2000 vert. Had to replace the vacuum motor on the drivers side to fix the problem. I was lucky to have GMPP for waranty to fix the problem.

GettnBetter

By chance did they indicate the GM part# of the replacement part?

GettnBetter

Dove into the problem a little this weekend but had to stop, ran out of time. The noise seems like it's coming from right behind the instrument console to the left of the stereo. Everything appears to work, just makes a constant hissing sound with everything turned off and the engine running.

DanTTVette

Any luck?

I just started with the same symptoms - hissing right behind dash temp sensor - varies with my right foot position. also depends on AC vent settings.

Blue Blood

I've got a constant hiss coming from behind the dash that goes away when I turn on the AC. So what's the difficulty level to get to this area, and is it best from the front or under the dash?

Thanks,
Clint

Bill Curlee

PM me your email address and I will send you the valve schematic so you can troubleshoot the issue

00Corvette

The spot you guys are describing is exactly where that little "muffler" resides in BC's pics.

To the left of the stereo about 10 inches to a foot behind the interior air temp sensor.

DZ

and it really depends on where your vacuum leak is coming from..most of the AC system is probably accessed easiest by pulling the dash and going at it from the top. Some have changed their actuators and done some re-connecting of vacuum lines from underneath. It will literally only take about 45 mintues to pull the entire dash off. Maybe an hour your first time but only if you really take your time.
Once the dash is off, just about everything is sitting right there in front of you.