To start off my car is a 1989 with the electronic controls. I just noticed that my clutch for the A/C will not engage after doing my header swap. So due to previous posts on the forum and general electrical knowledge I have narrowed it down quite a bit. So my findings are that I am not receiving a ground at the green wire at the clutch coil. If I manually jump the wire to ground then it engages and all issues are fixed but me making a random jump wire is not a repair I like. I pressure checked my system and it checks fine and I also jumped the high and low pressure switches and it made no difference for engaging the coil. When I check the black wire for voltage I see the 12v I should be getting but I am also getting 4v on the green which leads me to believe there is an open ground.

My main question is where does this ground go to and is it possible I knocked something loose doing the headers?

I also checked for continuity from the green wire at clutch coil to green wire at blower control module and continuity is good there. It’s after that point where I lose where the wire goes to as the diagram in the book is not very clear where it goes to me.

Thanks in advance for any help.

 

Just an update. I replaced the blower motor control module and it worked great for 2 days and just quit working again. Same issue where the coil isn’t engaging the clutch. I’m wondering if it’s a bad part and died after the 2 days or if maybe I have another issue and am overlooking it and that’s what killed the new BCM.

Some input would be awesome on this. Thank you.

 

I'm going off of poor memory, but isn't there a compressor clutch diode in that system? If so you should verify it is not bad. Diodes prevent arc back to switches and modules when the field is broken in the clutch coil and creates a spark - can easily be 80-100v spike. If the diode has failed, you could be killing components from the spark coming out of the coil when the field collapses.

 

I just got out there and checked the diode and it is reading properly. Roughly have a colt one way and nothing going through the other way. The orientation of the diode is with the gray band towards the black wire and the solid black end on the green wire. If I’m not mistaken that is the correct direction too. Also I could be wrong on that lol haven’t played with diodes in quite a while

 

On the C68 electronic climate control the black/white wire is always hot when the ignition switch is on. The switching is done with the ground wire. On the early c4's The compressor control relay is located in the blower control module. It closes when it receives a signal from the heater and a/c control assembly.

 

Ok everyone so I hate to admit it but I overlooked something super simple which is good because it led me to another issue. So the fuse blew for it and what made me look there was my coil stopped working. Would not engage the clutch even when I jumped it with power and ground. I took everything apart and found out that the pulley had literally eaten through the coil to where I could see copper wire. That’s what made me realize it mustn’t have shorted and blew a fuse. I put the old coil back on and replaced the fuse and everything is good to go. Will have to buy another new coil tho because the old one is weak and has a high ohm reading which I don’t like but it will do for a few days while I’m gone and can’t drive it anyway.

Thanks for the help guys. Hopefully this will help future people too. Just gotta figure out why that pulley ate the coil. Both were brand new and came as a kit.

 

I don't know if this will help but my compressor clutch wasn't working (but I was also low on R-12) the owners manual for my 1992 said if I pulled the A/C fuse and the radio fuse at the same time and hold for a minute the clutch will in gage, and it did but I still had to ad R-12. Keep in mind mine is a 92 good luck.