another 94 AC controller question
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Joined: Oct 2011
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another 94 AC controller question
i have searched and read through a ton of threads on this subject but haven't seen my exact issue. Our 1994 C4 that we are rebuilding has the C68 electronic controller that had the typical power loss and freeze-up of the controls on power head. I sent controller and programmer to Bryan at Batee.com and he confirmed they both had bad caps and he rebuilt them both. I re installed them in the car and all functions work flawlessly, except the command signal to compressor clutch is for the lack of terms, "inverted". All zones coincide with their buttons, but the compressor only turns on when you press OFF, Vent, etc.....everything that isn't supposed to have compressor function does, and vice versa. Defrost, max, auto has no compressor trigger. Has anyone else experienced this? Bryan has been great, sending schematics, and suggested maybe the PCM was the issue....however i have the original to the car and a new PCM and it is the same for both. I have the FSM as well, and have verified signal from programmer to PCM, but as stated, signal happens on the opposite buttons it should.
not sure what to do, i just can't see how anything except the programmer could cause this. maybe it has a diode or something back feeding? not sure how to test the communication between head and programmer.......
not sure what to do, i just can't see how anything except the programmer could cause this. maybe it has a diode or something back feeding? not sure how to test the communication between head and programmer.......
Melting Slicks
Joined: Jun 2014
Posts: 2,236
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From: NJ
I can't help you with troubleshooting, but there may be a work-around to this problem. You could place a five pin relay (with N.O and N.C. contacts) to feed the compressor using the normally closed contacts of the relay to feed the comp. clutch. The signal from the C68 will power the coil of the relay. Sequence of operation is; when relay coil is energized the relay opens it's contacts and cuts power to the comp. clutch. When relay is de-energized the reverse will happen. (contacts close and powers Comp. clutch. ) A switched power source (hot with key on) will be needed to power compressor clutch. I have never tried this before, but in theory it should work. That's all I got!
Melting Slicks
Joined: Jun 2014
Posts: 2,236
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From: NJ
Ok so then what's your course of action? Better call an automotive diagnostician, but even then, I think the troubleshooting may surpass their abilities. This would be a device level repair meaning as in circuit board device repair/replacement. Most likely replacement as most modules are epoxy sealed. Good luck let us know your progress.
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Joined: Oct 2011
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Ok so then what's your course of action? Better call an automotive diagnostician, but even then, I think the troubleshooting may surpass their abilities. This would be a device level repair meaning as in circuit board device repair/replacement. Most likely replacement as most modules are epoxy sealed. Good luck let us know your progress.
Melting Slicks
Joined: Jun 2014
Posts: 2,236
Likes: 497
From: NJ
I am an ASE certified master tech with over 30 years' experience and this has me stumped. That is why i was inquiring here to see if any Corvette owners have ever run into this. I do not have a GM tech 2 diagnostic computer as we are a small restoration business with normal focus on older classics. I would prefer to find the issue before i try any last ditch modifications.
I have never run into your problem.
Sounds like the problem still lies within the controller. Like an EPROM is programmed incorrectly. But here again we're getting into device level repair which is doable but finding the offending device is the hard part and without proper equipment near impossible. For now, I would inspect the controller and look for Capacitor values., breaks/ shorts in circuit board paths, resistance values, inductor values. Looking for anything out of range. Other than that, there's not much more you can do. Maybe go back to Brian at Batee and pick his brain some more or have him re-test the modules. Good Luck, this is a real head banger!
Thread Starter
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Joined: Oct 2011
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Well you are ahead of 90% of the owners here with those credentials.
I have never run into your problem.
Sounds like the problem still lies within the controller. Like an EPROM is programmed incorrectly. But here again we're getting into device level repair which is doable but finding the offending device is the hard part and without proper equipment near impossible. For now, I would inspect the controller and look for Capacitor values., breaks/ shorts in circuit board paths, resistance values, inductor values. Looking for anything out of range. Other than that, there's not much more you can do. Maybe go back to Brian at Batee and pick his brain some more or have him re-test the modules. Good Luck, this is a real head banger!
I have never run into your problem.
Sounds like the problem still lies within the controller. Like an EPROM is programmed incorrectly. But here again we're getting into device level repair which is doable but finding the offending device is the hard part and without proper equipment near impossible. For now, I would inspect the controller and look for Capacitor values., breaks/ shorts in circuit board paths, resistance values, inductor values. Looking for anything out of range. Other than that, there's not much more you can do. Maybe go back to Brian at Batee and pick his brain some more or have him re-test the modules. Good Luck, this is a real head banger!
oh, and the zones all match the function you press so vacuum components are good...just the inverted compressor signal
