Weird noise in dash

[chevyman5573]

I have a '95 full-size 4WD. For some time now, I'm getting this strange groaning sound from under the dash. I think it's the damper/flapper mechanism for the AC/heater. It constantly groans, then a dull snap, like a diverter flapper closing. It continues to repeat the process all the time you are driving. It also continues after killing the engine and turning the ignition switch back on. It quits after a while, probably after the vacuum reserve is gone.

Any suggestions on what this might be, what I need to remove/replace and how to get there?

Thanks!

[Bob T]

I don't know how the dampers are operated in your year truck.. If they are vacuum operated there could be a vacuum leak.

The oddest noise I have ever heard from a dash is when one of our company vehicles (parked next to the woods) got a family of mice in the vent duct. When the heater was turned on there was a great squealing and squeaking, followed by mouse parts flying out of the vents.

[someotherguy]

I don't know how the dampers are operated in your year truck.. If they are vacuum operated there could be a vacuum leak.
88-98 trucks with AC have electronic motors for all the modes; there's three of them. Hot/cold mix, fresh air/recirculate, and defrost/floor/etc.

It could be any of the actuators, or the control head itself. At least you can start troubleshooting by finding out which one is doing it. You can watch the defrost/floor/etc. actuator run if you poke your head up under the dash, above the driver's side of the transmission hump. The hot/cold mix is over about another foot towards the middle of the ac/heat ductwork box, about dead center of the dashboard. That one should be pretty obvious if your temperature setting isn't staying constant. The final one, and what seems to be the more problematic (and hardest to reach) is the fresh air/recirc actuator; hiding at the far passenger side, crammed sort of between the firewall and the ac/heat ductwork box. It's a PITA to reach/see.

The oddest noise I have ever heard from a dash is when one of our company vehicles (parked next to the woods) got a family of mice in the vent duct. When the heater was turned on there was a great squealing and squeaking, followed by mouse parts flying out of the vents.
Funniest thing I've read all day. :D

Richard

[chevyman5573]

I think the last and most difficult possibility is probably where my problem is. The temperature stays steady, I looked at the control over on the driver's side and it is going through the motions like it should. The sound seems to be coming from the location you described somewhere behind the glove compartment and the firewall.

It has been making these sounds for some time and it seems to cycle between normal air and max air, which seems to agree with the fresh/recirc air situation you described also.

Any suggestions on how to minimize the work to dissect the plastic in this area and get to the problem?

Thanks

[someotherguy]

I posted a write-up on it with pictures but it was on the 88-94 style dash. The ac/heat ductwork box is the same on 95-up but the dash is different, so I don't know for sure if it's possible to do it the same way, but it SHOULD be. Lemme find the post and I'll edit back and link it here.

Here's the thread I posted it in: http://www.fullsizechevy.com/forums/general-discussion/interior-tech/343208-c.html

Though normally when this thing goes bad it makes a knocking noise for a few minutes every time you start the truck or turn it off. Yours may be bad but just behaving differently...or again, it could be the control unit for your ac as the 95-up style seems to be a real POS.

Richard

[chevyman5573]

I think my '95 is just like the photos you sent. This has been incredibly helpful and I can't thank you enough for all the inforation. I guess it's time to jump in and put my patience to the test.

Thanks again,
Holden