[Spinman]

I've been having problems with the HVAC buttons on my '90 practically since it was new. Decided that it was time to solve the problem and put the problem behind me....

The buttons seem to operate with a mind of their own - sometimes they work, sometimes they don't. I can turn the car off and on, same problem continues to exist. I can wait it out - sometimes 20 minutes, sometimes 2 days. But eventually they become functional again (and perhaps another becomes temporarily non-functinal).

I've been told that '89 and earlier dashboard push buttons need to have the button contacts cleaned from time to time to ensure that theyare operating properly. '90 and later should not require cleaning, the design was changed. Don't know if this is true or not. I've never tried to clean my buttons.

The same source suggested that I unplug and replug the HVAC programmer and see if that solved the problem. If it didn't - it was most likely that I needed a new programmer.

I did just that, and all buttons started to work again. Several days later, the problem returned. Each day, it's a different button that refuses to work... Today the off, AC and recycle buttons are not working - everything else is. In the past, temperature and fan control buttons were also affected.

I'm currently shopping for a programmer - I wish there was a definative test to confirm that this is in fact the problem...

Anyone have an opinon? With programmers running $300- retail, I don't want to swap units and have the problem remain!

The unit seems very flimsy and not that technical (on the outside). Wonder why its so expensive.

Anyone know if there is a repair station to send the programmer to for analysis, testing and rebuild?


Any other possible problem area - vacumn leaks, bad valves, button cleaning?

Thanks -

 

[Spinman]

I just performed a scan of TSB's for the '90 Corvette and ran across # 903781-A issued Nov '90 titled "Loss of Heating / Cooling Control".

Does anyone have subscription access to this TSB?

Wondering if the loss of control referenced in the title reflects the button control problems I am experience (and what the prescribed solution might be).

903781A NOV 90 A/C - Loss of Heating or Cooling Control


Thanks -

 

[Patrick]

I don't have access, but Vettetech91 is a Chevy mechanic at a dealership. I bet he can get you the info you want. I'd send him a PM and get his ass over here to help, he's been AWOL. :thumbsup:

 

[FiberglasMD]

MY 94 had button problems. Usually the temp. would not adjust. I replaced the control head. I got it from chevrolet. I think it was $300+ at wholesale. That fixed the problem. So far never bothered since. Chevrolet took my old one back for a core exchange.

 

[Spinman]

Out of curosity - how did you determine that the problem was with the control head and not the programmer?

Did your buttons constantly fail - or was the problem intermittent -as is mine?

I've been wondering if I should remove the control head the check the continuity of the switches with a VOM...

 

[FiberglasMD]

Somewhere I read abot the C-68 button problem on the 94. Sometimes the temp would adjust, other times it would not. So I replaced the control head.

 

[Spinman]

It's a slow week -

I decided to bite the bullet and remove the C-68 Electronic HVAC control head ('90) to see if I could notice anything obviously not functioning properly as part of my diagnostic check list.

1) Removed Center Console
2) Removed Center AC Vent
3) Removed Stereo Trim Bezel
4) Removed Right mounting screw on Radio Head
5) Removed Left mounting screw on AC Control Head

I'm unable to reach right mounting screw on the AC Control Head - I'm unable to push the foam dash far enough away to seat the drive socket (at least as far as I feel comfortable without fear of breaking the dash).

Any suggestions as to how I could reach this final bolt?
(And once this screw is removed, will I have enough room to pull the head out w/o hitting the dash?)

Do I need to remove the upper dash pad (if so, how?)
Do I need to remove the lower padding on the passengers side that is attached to the console (if so, how?)

Or is it just a matter of constant pressure to push the dash far enough to insert the socket.....?

How easy was your installation?

Thanks for your suggestions...

 

[Spinman]

Just ran across the Diagnostic Flow Chart for the C68 Electronic HVAC in the Shop Manual for the '90 C-4 (page 8A-62-5).

This appears to be the checklist I have been seeking that will help me determine if my problems are programmer or control head related (or heaven forbid - radio control head...yuck).

99% of the tests appear to be checking for wiring shorts or open grounds using a test light attached to pins on the control head wiring harness (with programmer sometimes attached and sometimes disconnected).

The final test is the one that is probably the most interesting - attach a scan tool with E & C capabilities to the ALDL connector and control HVAC functions with the scan tool.

If there is no control - replace the programmer.
If there is control - replace the control head.

Can you recommend a home mechanic priced E & C scanner - or should I have the dealership do a scan for me....?

 

[-=Jeff=-]

I would suggest the Dealer for testing the E & C Bus. the testers are too pricey for the consumer..