Let's try this again.
I got into car today (94) and found that the ac controls were unresponsive. The ac was working....blowing ice cold.....but I could not turn off, reset temp, change from "auto" setting, etc.

Any experience with this problem?

 

...could be "dirty"....but, try this; disconnect battery for a few minutes and see if that helps (if you haven't already done that)...i think that there is a diagnostic section on this item in the field service manual...

 

I seem to have issues changing the temp on mine?? See what comes of this

 

will give it a shot when I get home this evening.

 

No luck.......tried following suggestions in owner's manual to "reset" the system and also tried your suggestion to disconnect the battery.....no change.

The darn thing is blowing ice cold......changes speed automatically like it should, I just cannot over-ride it manually and turn off, set fan speed, or get a reading on the LCD temp screen.

Any other ideas?

 

My 94 does this too, occasionally. Seems one of the fan speed buttons is dirty and is sticking. To get mine back to life I just press real hard (not beat on) the fan up and fan down buttons (one at a time) and it magically comes back to life. Guess I need to pull it apart and clean the buttons. I think it is only one of the two buttons but it happens so rarely that I don't remember which one it actually is. Hope this helps..

 

The control head needs to be dis-assembled and cleaned.

Behind the buttons is a rubber membrane, with small carbon 'buttons' attached to the back side. As a button is depressed, it presses these 'buttons' against the circuit board making contact between two small strips of gold. However, what most don't realize is that the circuit board is not a relay for controls, but sends digital signals to the control unit. Hence why it acts up in odd ways.

It requires gentle dis-assembly, gentle cleaning of the carbon 'buttons' (alcohol and cotton swab) and of the circuit board contact points (alcohol and cotton swap or gently with a pencil eraser.

 

I will give it a shot.
A new unit runs about $270 dollars.......tempting to go ahead and replace while the original is out.

While the car is a '94, I just rolled 46,000 miles on this week......hard to believe it is dirty / worn out.

 

Thanks for the suggestions on cleaning.......but it did not correct the problem....still unresponsive and no reading on the temp screen.

SOooooooo, picked up new part today. Rather than disassembling dash again, I plugged in to check first......same results.
Brand new $300 unit and it is not working. This tells me that my diagnosis must be incorrect......which is funny since the guys at the Vette shop concurred with my diagnosis.

Guys please help me out here. I have checked all fuses and cannot locate the problem.

 

Have you done any trouble shooting? Does the unit have power?

 

Has power......lights up....just dashes across screen where temp should read....and none of the buttons will work.....to change fan speed, or change from floor to vent or etc.

 

Do you have the FSM for the '94? I see a section on DTC 10 OR "---" that seems to be possibly your problem, as you indicate you're seeing "---".

This section says that "---" will be displayed when the HVAC control head does not receive "E" and "C" data from the HVAC programmer when expected after ignition is cycled "ON". Terminals C13 and C14 on the HVAC programmer and C4 and C5 on the HVAC control head are related to this serial communication. You may have a bad connection somewhere in the system.

Another possibility is the HEATER and A/C PROGRAMMER, the device that's connected to the Head Unit via the serial communications. Could be a problem with that.

I can scan this for you tomorrow if you need it.

 

Thanks for going to such trouble. I do not have the book that you referenced. Any suggestions on where it can be picked up?......and to show my ignorance, what is "FSM"?

 

No trouble at all . Factory Service Manual (FSM). You can buy them used off of ebay, if you can find them. Right now I don't see any for sale. You can search the forum for other sources for purchase. Unfortunately I'm at work now and my FSM's at home. I'm traveling Thurs and Fri and won't be able to do any scans till next week. If you still need the scans, let me know.

Just remembered much, but not all, of the information from the FSM can be purchased online at http://www.alldatadiy.com/buy/index.html. I have a subscription for the '94 vette and just checked the information regarding the A/C. What I read last night in the FSM seems to be there online.

Keep us posted .

 

Well I bought into the subscription and still am not getting anywhere.
I have an aquaintence who has an AC shop and says he has never heard of this type problem.

If you have better info than the ALLDATA site, like something identifying where the AC Programmer is and how to test it, maybe that is the culprit.......got to be a better way.

 

There is a way to trouble-shoot the problem with the C68 climate control.
It requires a Vetronix Tech-1A scan-tool (the same tool GM dealers used for years) and some jumpering of wires -- this is all in the FSM.
There are two serial buses:
1) Serial bus for the radio control to communicate with the receiver.
2) Serial bus for the C68 climate control head to communicate with the programmer.
By jumpering these two buses together, the Tech-1A scan-tool can access the C68 bus on the ALDL connector.
Once these buses are jumpered, you can use the Tech-1A with the "body" cartridge to diagnose the problems with the C68 climate control.
Things you can do once the Tech-1A is able to access the bus:
1) You can simulate the control head with the Tech-1A and send commands to the programmer to see if it responds.
2) You can monitor the commands (in plain English) from the control head to the programmer to see if the control head is functioning correctly.
This eliminates guessing.

After diagnosis, you are supposed to remove the jumper on the buses.
What I did was run the jumper through a small switch so I could easily connect the buses and diagnose the system and then disconnect it easily.

Tom Piper

 

I had the same problem, Ac control not working. Two things you can do. First, take the control out and clean the contacts inside. Or second, buy a used one from ebay or from someone here in the forum. I bought mine from the forum for about $45.00. Works perfect now.

 

Yours was the same problem? It had power to it but would not control anything or even give a reading? You just plugged in new one and it worked?

 

not to throw in useless info, but a reason your car probably is blowing cold is that there is no reference from the temp sensor that tells the module that the car is either cold or hot.
Usually a temp circuit uses a wheatstone bridge type of electrical circuit that uses one leg as a variable resistor (temp sensor) low resistance as hot and high resistance as cold. (google wheatstone bridge to get an idea of what I'm talking about)
It sounds like a connector is mildly corroded, or electricallly dirty, or you have lost a ground from a hard ground point.
These can be hard to find, but since you bought the subscription, look up the chassis grounds under the dash or in the kick panels, and either use 400 grit sand paper, or some scotchbrite, and clean the ground locations. just tear off a corner of the sand paper, and clean the wire and the place it screws to.
Doesn't sound as glamorous as buying a part that smooths out the problem, but in my experience, it's the little things that get ya.
Your problem totally sounds inexpensive to fix, just frustrating.

 

Well I spoke to another vette specialist yesterday who immediately told me he has seen the problem many times......He said most folks do immediately assume the control head (Climate Control Unit) is the culprit. However, more times than not is is the AC Programmer (on firewall, under dash near steering column) He also shared that although he has equipment purchased to track down / anyalize the parts, the equipment was a waste and frequently provides false reads.

So, I have started the search for a new programmer.....am told that it will have to be a GM Remanufactured......that the parts are no longer produced...... Does anyone have info to refute that?