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Did this recently. Worked great. Solved my "mind of its own" control unit behavior on my 95. Not sure it will solve yours. But after 20 years, the contact build up residue. And you'll see it as soon as you get it apart.
Originally Posted by Opihi59
Okay, knowing what to look for/look at is helpful, but sadly I have nothing definitive to report. I did manage to get my unit to go to the OFF position but it never started blinking over multiple tries either with key to RUN, or actually starting it. I took several drives of adequate speed and duration to try to "reset" but achieved nothing else. I did get varying outside temps between 82 and 74. On one occasion the off light got very dim, but didn't flash. What happens is that after waiting 20-30 seconds to see if it will flash, engine on or off, the fan will start blowing gently, and putting out air from the defrost vent as well as the foot vents. On some tries, I can hear the compressor kicking on and off, and if it is running the air will be cold. I will let it sit overnight and try again in the morning. It is not making sense at all, and is inconsistent in everything but being broken. I can't make any connection to having removed the neg battery terminal and fixing my instrument cluster, but I cannot help but realize it was working fine before this, and doesn't work now.
I did find this video, wherein the author had non-responsive buttons on his head unit, and repaired it by disassembly, and cleaning contacts with a pencil eraser. I will likely do that tomorrow to make sure that isn't the issue, and it is a simple enough process once you know what to do. This Video
I also got the idea to create a fault code by disconnecting the outside air temp sensor, then running the diagnostic test on it again to see if I can get the OFF light to blink, and then interrogate for code 03, just to see if that mode will function. I was able to press both fan speeds down 5 seconds and get it to display OO, and could scroll up and down thru codes. But on another try following a short drive, it displayed - - Of course none of this is helpful. I'll post back in after I try cleaning contacts on the head unit tomorrow.
Did this recently. Worked great. Solved my "mind of its own" control unit behavior on my 95. Not sure it will solve yours. But after 20 years, the contact build up residue. And you'll see it as soon as you get it apart.
Just did this to my 94 a few hours ago, worked great.
AC controls work perfect now!!! Tom
Trying the eraser action to the contacts of the head unit is a reasonable first step as it is comparatively simple, and if successful will save you a ton of annoying effort to address the AC programmer. If cleaning contacts on the head unit does not work, you're going to be diving into the dark reaches of under-the-dash to replace capacitors on the programmer board.
Thank you for the thread. The pictures are very helpful in understanding the under dash Programmer module and both the electrical and vacuum line connections to it. There is another thread that is a good resource for removing the hvac climate control programmer. There are two methods to getting to the circuit boards inside the HVAC Programmer Module so they can be removed for repair. One way involves removing the entire programmer module and that means detaching both the electrical plug (held on with a single latch if it hasn’t snapped off) and the green vacuum line manifold that is held on with the push on nut. Taking the entire programmer module out method is the most time consuming and challenging. Batee.com has a video showing the process. The other method is to remove the electrical plug only, rotate the programmer module plastic case in such a way that the back open section of the case is oriented towards the floorboard and then you can just remove the 2 screws from the small top vacuum solenoid circuit board and then the 2 screws holding in the larger main green circuit board. Just make sure your electrical plug is already undone before removing the circuit board screws because the main board is not going to drop out of the case with the plug attached and you will need the rigidity of the secured boards to wiggle the plug off. The second removal method where you just remove the boards saves you a lot of time and frustration. However which removal method you undertake will depend on your particular Programmer failure symptoms. If it’s only an electrical failure of the Programmer then the boards only method is fine. But but if you have signs of vacuum leaks (actuators not moving, or air blowing out the floor and defrost vents instead of toward the driver), the programmer may have internal vacuum issues, in which case Batee.com recommends removing the whole Programmer and sending it in for repair. If you do have electrical only issues and once you have the boards out of the module case you can initiate your own component repairs or just send the boards to the batee.com folks for professional repairs and refurbishment. I sent my boards to batee.com as all this soldering was way beyond my skill level. Batee.com will replace all the capacitors and other high failure parts, and install new solenoid filters, and send you back a fully refurbished, tested and working Programmer / boards.
There is the other post on the removal process I wanted to link to help others find it:
This is an excellent thread that lists all of the return codes and their meaning when you run the C68 Climate Control’s diagnostic function (holding the up and down temperature buttons simultaneously to activate the testing)
Here is a YouTube video that describes the symptoms, the diagnostic process, shows how to go about removing the Programmer circuit boards and provides an overview on the anatomy of the Programmer module:
This is a pin out chart for the 1990-1996 HVAC Programmer. You may notice on your car year’s wire harness the colors don’t match up to this chart’s colors. Its best to use the Electrical Supplement section of the Field Service Manual (FSM) for your car’s exact model year to get your colors to match. But I think you will find the wire description / function to be the same as this chart. This is the wiring harness from a 1993 Vette. The D1-D16 wire colors mostly match the chart but not 100% (D15 is dark green on the harness and noted at dark blue on the chart). But the ports used for wires and ports that are empty match up perfectly. Use the FSM Electrical Supplement for your car’s model exact model to year to get a model year specific chart. FSMs can be bought and download from multiple online marketplaces. Just make sure you get the electrical supplement with it.
Last edited by jeanpreston; Feb 28, 2026 at 01:29 PM.
Just did this to my 94 a few hours ago, worked great.
Tom
