94 A/C Clutch
Thread Starter
7th Gear
Joined: Aug 2009
Posts: 7
Likes: 0
From: Mooresville NC
94 A/C Clutch
94 with C68 electronic climate control. I cannot get the A/C clutch to engage correctly. It will engage if I manually jumper the a/c relay. All functions on the control head work perfectly, just no a/c clutch in any mode that requires the a/c to be running. Here is what I have diagnosed already.
No codes in PCM or C68 Control head
Already tried disconnecting batt for 15+ min.
Jumping or grounding low pressure switch does not engage. No voltages at either pin on the low pressure switch connector.
5V ref voltage present at 3-wire high pressure switch. No voltage in any other wires. (I know one is ground).
A/C relay is brand new.
85 & 87 on the relay connector have good voltage. Jumping 85 to 30 engages the clutch.
Thanks to anyone who can help out!
No codes in PCM or C68 Control head
Already tried disconnecting batt for 15+ min.
Jumping or grounding low pressure switch does not engage. No voltages at either pin on the low pressure switch connector.
5V ref voltage present at 3-wire high pressure switch. No voltage in any other wires. (I know one is ground).
A/C relay is brand new.
85 & 87 on the relay connector have good voltage. Jumping 85 to 30 engages the clutch.
Thanks to anyone who can help out!
Thread Starter
7th Gear
Joined: Aug 2009
Posts: 7
Likes: 0
From: Mooresville NC
I'm not sure on the R-134 level, but I thought bypassing the low pressure switch would verify that it's not a low freon issue? What would be the best way to verify if the ECM is getting an a/c signal from the programmer?
Thank you
Thank you
Pro
Joined: Aug 2009
Posts: 725
Likes: 4
From: Plano, TX
Press the up and down temperature buttons simultaneously for 5 seconds to enter diagnostic mode. The LCD will show 00. Now press the auto button and it will give you C68 fault codes. Code 9 is Low Refrigerant.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Ok….Problem in your write up is connecting 85 and 30 on the relay. Your putting 12 volts directly to the clutch which only proves the clutch is OK. It does not activate or prove out the relay which would puts the 12 volts thru it to the clutch. If you ground pin 86, that should activate and close the relay engaging the clutch. Grounding pin 86 is what the PCM does to active the relay and engage the clutch.
Grounding pin B of the cycling switch is what the programmer does to the PCM. So if you did that and had a good connection, then you can eliminate the programmer at this point.
So, if the relay works OK by grounding pin 86, then the item between the pin B (wire 762) and pin 86 (relay) (wire 459) is the PCM. It doesn't sound like it is activating the relay when the A/C request signal is applied to it, wire 762.
If this scenario if correct, then the PCM is bad or there is a bad pin connection in a connector. I would spend my time initially looking for a bad connection. Although possible, I think the odds of a bad PCM is low.
Do you have any drawings or documentation on the A/C system?
Grounding pin B of the cycling switch is what the programmer does to the PCM. So if you did that and had a good connection, then you can eliminate the programmer at this point.
So, if the relay works OK by grounding pin 86, then the item between the pin B (wire 762) and pin 86 (relay) (wire 459) is the PCM. It doesn't sound like it is activating the relay when the A/C request signal is applied to it, wire 762.
If this scenario if correct, then the PCM is bad or there is a bad pin connection in a connector. I would spend my time initially looking for a bad connection. Although possible, I think the odds of a bad PCM is low.
Do you have any drawings or documentation on the A/C system?
Last edited by pcolt94; Sep 29, 2011 at 10:45 PM.
Thread Starter
7th Gear
Joined: Aug 2009
Posts: 7
Likes: 0
From: Mooresville NC
Thank you for the detailed response. I just replaced the programmer because I had the typical windshield/floor only air control, but the compressor would engage when it was suppose to. I found a new AC Delco programmer and that fixed my air control issues, but now no A/C clutch engagement. I'm wondering if that part replacement is somehow related to this issue now.
I did try grounding each pin on the low pressure switch and that did nothing.
I guess I'll have to dig deeper and check voltages out of the programmer and PCM.
I did try grounding each pin on the low pressure switch and that did nothing.
I guess I'll have to dig deeper and check voltages out of the programmer and PCM.
Pro
Joined: Aug 2009
Posts: 725
Likes: 4
From: Plano, TX
BTW the AC request signal can be monitored by a datalog.
Last edited by 93VettePilot; Oct 1, 2011 at 06:43 AM.
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Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Although it will be a pain in the A**, you changed the programmer, fixed one item but then something else did not work. At that point I would back up one square and connect the original programmer. You do not have to connect the vacuum lines but only swing over the electrical connector. Then check to see if the clutch engages. If it does, then maybe the new programmer is bad or there is a bad pin connection on it.
You only need to ground the green/white wire of the low pressure switch. Probably not a good idea to ground the other wire (dark blue).
If there is no change with the original programmer in there, then something else possibly happened. But grounding the green/white wire should active the PCM to close the relay and engage the clutch.
Always look where you were working to see if you disturbed something, connector or such. If the clutch worked, and you did not do anything else, and then replaced the programmer, I would definitely target the programmer and area as a starting point.
Make sure your 10A clutch fuse is still good.
It would also be good to know if grounding pin 86 of the clutch relay activates it and that portion is working OK.
You only need to ground the green/white wire of the low pressure switch. Probably not a good idea to ground the other wire (dark blue).
If there is no change with the original programmer in there, then something else possibly happened. But grounding the green/white wire should active the PCM to close the relay and engage the clutch.
Always look where you were working to see if you disturbed something, connector or such. If the clutch worked, and you did not do anything else, and then replaced the programmer, I would definitely target the programmer and area as a starting point.
Make sure your 10A clutch fuse is still good.
It would also be good to know if grounding pin 86 of the clutch relay activates it and that portion is working OK.
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Joined: Dec 2009
Posts: 4,363
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From: Birmingham Al
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Thread Starter
7th Gear
Joined: Aug 2009
Posts: 7
Likes: 0
From: Mooresville NC
Put the old A/C programmer back in and the compressor worked correctly.
Apparently I have 2 bad a/c programmers in a row, with one of them being a brand new AC Delco unit. One does not respond to control head inputs for vacuum control, and the other works perfectly except sends no a/c signal out. Good example of the "curve-*****" this car can throw at you sometimes. I guess I'll try to find a 3rd programmer hoping it is fully functional. Kind of a pain considering this part averages around $400 and is a bit difficult to find new.
Thanks for the input guys!
Apparently I have 2 bad a/c programmers in a row, with one of them being a brand new AC Delco unit. One does not respond to control head inputs for vacuum control, and the other works perfectly except sends no a/c signal out. Good example of the "curve-*****" this car can throw at you sometimes. I guess I'll try to find a 3rd programmer hoping it is fully functional. Kind of a pain considering this part averages around $400 and is a bit difficult to find new.
Thanks for the input guys!
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Put the old A/C programmer back in and the compressor worked correctly.
Apparently I have 2 bad a/c programmers in a row, with one of them being a brand new AC Delco unit. One does not respond to control head inputs for vacuum control, and the other works perfectly except sends no a/c signal out. Good example of the "curve-*****" this car can throw at you sometimes. I guess I'll try to find a 3rd programmer hoping it is fully functional. Kind of a pain considering this part averages around $400 and is a bit difficult to find new.
Thanks for the input guys!
Apparently I have 2 bad a/c programmers in a row, with one of them being a brand new AC Delco unit. One does not respond to control head inputs for vacuum control, and the other works perfectly except sends no a/c signal out. Good example of the "curve-*****" this car can throw at you sometimes. I guess I'll try to find a 3rd programmer hoping it is fully functional. Kind of a pain considering this part averages around $400 and is a bit difficult to find new.
Thanks for the input guys!
I now wonder why the compressor did not start when you grounded the B wire from the cycling switch. That should have worked and now it bothers me as to why not.