i have a problem with the a/c controller in my 94.

the symptom is that it appears to reboot, but there isn't a computer in it, so i'm not sure what exactly is the problem. i'll be driving along, the window will show the outside temp. suddenly, the digits disappear for a variable amount of time, then show the inside temp setting, and go back to showing the outside temp. the green lights over the selected button also goes out at the same time. when it comes back, it is always selected in the mode it was in when the power went out.

it never loses complete power, because the backlight for the temp window is still on.

the time period between outages is variable. the roughness of the road isn't the cause, since it happens on both smooth highway, rutted roads, or on the dirt road that leads to my house, and doesn't occur on a sudden jolt (hitting a pothole, for instance). the time period that it stays off is also variable. sometimes it just flickers off/on in less than a second, and sometimes it stays off for minutes.

when this first started happening, if i hit one of the buttons a few times, it came back. that doesn't work now. sometimes, when it was operating, it didn't respond to any button presses so i couldn't change either the mode or the temp level.

i took the controller out, and then took it apart. i cleaned the contacts behind all the buttons (which did solve the non-working button problem pretty much), but did not cure the off/on problem.

the a/c and heat works normally and well when the controller is actually working.

is there a relay that provides power to this module that could be a problem? could it be a flaky temp sensor? the fuses are not loose, and good for it, as it does work ok sometimes.

it really does act like the car was turned off/on that is causing this, but occurs when driving.

 

Sounds like you were on the right initial track to solving the problem. I would also clean the pins that connect the main board to the other vertical card. Use the cleaner (alcohol) and a Q tip or applicator to clean the pins real well. I try to get some cleaner in the socket also. DRY thoroughly before re-assembly (use dry can air). Also clean the connector plug on the rear of the unit.

On my unit I also re-flowed the solder where the LEDs are and buttons due to varying intensities. But that is an option only for the competent. The main circuit card is a coded card so most of the solder looks good and not usually a source of problems.

Of course the C68 units do go bad but many are repaired using these procedures and cleaning them up.

 

well, i happen to have a spare 96 vette (the wife's, hopefully she won't want to drive it today as it has a big hole in the dash), so i swapped out the controller from her car for this one as it is the same part #. it has exactly the same symptoms so i guess the problem is elsewhere.

bad wire, wiring harness, sensor, computer, ground? is the ground point behind the dash or somewhere else?

 

This is how I would approach the problem from your current position.

Re-install the 96 head back in the 96 car check it out, make sure it is still OK and not damaged.

Then install the 94 head in the 96 vette and check it out. If it performs normal, Then you can proceed forward in checking the 94 vette.

Hook up the 94 head in the 94 vette. Make sure beyond a shadow of a doubt that the connector (from the car) is making good contact and not the source of the problem. Then maybe tap around/wiggle wires and such that might be causing the problem in that area.

If no response to that, then I would pull the controller out (thing with a plug and a bunch of vacuum hoses) and give it a good internal visual inspection. There are a couple resistors in there that have been known to cause problems (might look discolored). Can’t remember what symptoms they cause, I don’t have my notes or books here currently.

That’s my opinion of where to start, you might end up deviating from my initial write up as you go down the diagnostic tree.

 

thanks for the tips.

"then I would pull the controller out (thing with a plug and a bunch of vacuum hoses)"

i take it you're referring to something besides the head when you say controller? the head doesn't have any vacuum hoses, just a wide plug with about 16 leads, iirc. where is this controller?

i have a shop manual for the 94 that came with the car from the original buyer. however, since this was a very early build (gm press car for 94), almost half of it says 'see the 93 manual for this section', and of course i don't have a 93 manual.

 

Your right, there is another box that is part of the environmental system. Think of it as an interface between the “head” and the blower fan and vent control. The controller actually applies the voltage to the fan assembly. It also has vacuum solenoids to direct the vents (airflow, where it comes out) positions. There are wires connecting between them as well as the serial data bus.

The controller is at feet level on the left of the drivers side (I believe). The shop manual should tell you where it is. (probably harder to find the pages than the controller). Check the plug on the controller for bad connection also.