1994 2500 Suburban-HVAC system-FINALLY FOUND THE ANSWER

The old '94 'burb doesn't get much use these days. It basically just sits outside and grows a botanical garden. This summer is proving to be good boating weather so I got it fired up and have been driving it around a bit. I even had to go get a set of used tires from the local Ruskie Tire shop because my 27k, 14 year old tires were rotting off of it and leaking air.

Everything has worked well except for today. I turned on the A/C. No cold. Examination showed that the clutch was not engaging so I assumed it was way low on refrigerant. I'll check that out later.

I pulled into the market and shut the engine off. All of a sudden it sounded like I had a woodpecker in the passenger well. Checking it out, it seems that one of the doors in the heater box was rapidly opening and closing. After a short while, it quit. I drove it home and pulled into the driveway and shut it off. The noise started over again. It did that for a short period, then quit. It did not seem to matter what position I had the HVAC controls in.

With the key off there could not be any electrical activity so I assume that it was possibly vacuum causing the doors to open and close.

Any ideas where I might look?

Re: 1994 2500 Suburban-HVAC system-FINALLY FOUND THE ANSWER

If you own one of these '90's burbs, trucks or Tahoe types, it will sooner or later happen to you. They did not make this easy to find. There are three different servo/actuators that control three different doors inside the heater box under the dash. It did not help that the names of these doors/actuators seemed to vary somewhat, which make it more difficult to find. I have a Chiltons manual and it was totally worthless.

It seems these actuators commonly break inside and when you turn the key on or off, they actually cycle to find their positions. The noise is caused by a broken gear inside that is slipping. After about 30 seconds the test times out and the noise stops. It is not caused by a door opening and closing as I had thought. The good news is that two of these actuators are fairly easy to get to and replace. The bad news is that the one that is broken in my 'burb was the least talked about, the hardest to find and the hardest to get to to remove and replace.

Mine is the one that controls the inlet air door. It is not located on the main box like the others. It is located down between the main box and the blower. It is actually on the snout of the blower as the duct goes back thru the firewall. There is very little room between the two assemblies to get to the 3 screws holding it on. After hours of searching the internet and posting on two different forums, my next project will be to try to get the actuator out!