88-94 Electronic HVAC Controls Messing Up

[Triplel40]

Hey, wondering if anybody has had this problem before and knows a fix, or has torn into the HVAC control box and might know what is causing it. Don't really want to replace the HVAC because so far the only place I've been able to find a replacement is LMC ($350 ). I have only seen a few at junk yards around here and even then I would be shooting in the dark trying to find on that would actually work.

Anyways, key on, lights off-Blower motor runs at low speed, like it always does when HVAC gets reset after losing power. HVAC display is dim and flickering. None of the buttons work.

Key on, headlights on-Blower motor still running at low speed. HVAC display completely dark, still no buttons work.

Tried pulling fuse to hard reset it, even disconnected battery for a few hours then hooked it back up. No change.

Probably gonna tear the box apart later this week and see if anything stands out. Anybody torn into these before and know what I should be looking for?

VIDEO OF WHAT IT IS DOING HERE:
http://youtu.be/WiH5exmfyJk

 

[Dr.Zoom]

I replaced some transistors in my 96. I know they're different, but I think in my searching I recall seeing some info on earlier controls and that they're not too different. I fixed my controls for less than $10. I'll look back through my history and see if I can find something.

 

[Triplel40]

Alright thanks, appreciate any help I can get.

 

[Dr.Zoom]

Here's a link to one of the things that helped me fix mine, but it does state the pre 95 is very different. It's not exactly what you need though. http://www.chevytalk.org/fusionbb/s..._session_id/29d6e7f257e4d4e6e5b5000822f3cc2a/

There's probably info out there for the pre-95's.

 

[someotherguy]

The 88-94 controls almost never go bad. Most likely you have a poor connection at the harness plug; remove it and spray some good contact cleaner (I like DeOXIT) on the card edge and hook it back up. Don't use anything abrasive.

If it does turn out to be bad, a used 88-94 control from the boneyard is almost always a good bet. They don't go bad all the time like 95-up.

Richard

 

[Triplel40]

Yeah I'll clean it up and see what happens. Hard part about getting one from a bone yard is because it is an 88 so its black. The 89-94 ones are grey, and a lot of of them have the recirc button which I don't need.

Sent from my 3Cylinder Geo Powered Smartphone

 

[someotherguy]

Yeah... compatibility-wise, I think 88-89 are the same, possibly 90 (except for being gray) but I honestly can't remember.

I've maybe seen just a couple that had gone completely nuts, and if I had cared to spend time going over them with a soldering iron I probably could have brought them back to life. But at the time I had a whole lot full of GMT400's to pick from so the customer just got a replacement unit and was on his merry way.

Richard

 

[Triplel40]

Well, got off work early today so I tore into it. Problem was dirt, period. The harness plug connections were filthy, and there was dirt packed in between the rubber "buttons" and the contacts on the board. Since the plate holding the buttons is pinned to the board, I just blasted the air compressor between the two layers at a low pressure. Everything works great now. Was a pretty simple tear down, and noticed that mine has JY markings on it so it must not be the original. Oh well, works like its supposed to now!

 

[Untraceable79]

I have a replacement HVAC unit, for my '90 K1500 (3 speed fan, no rec button) , out of a '94 (4 speed fan, W/rec button). The problem I have is, when I plug the newer one in, it works for about 30sec. the the screen goes blank and starts flashing. Has any one done this conversion?

 

[Macfluke]

so far I have not been able to make the switch to the one with the recir button work, but I tried it a few years ago and got the same results as you did... I caught the wild bug again a few days ago and that's what brought me here, so i'm working on it again... I will post if I find the solution...