So today I spent a small chunk of time scratching my head over an AC system. This one seems to be pretty rare, or people never make it this far before giving up and heading to a shop, so I thought I'd write it down for everyone to see.

Basically, the AC light would come on, no cold air, on further inspection, the AC clutch was NOT(edit) engaging. after running through a small check list of jumping the pressure switch, checking the relay, I learned that the main lead to the clutch goes directly to the relay, no ecm, sensors or control units in between, unlike the cooling fans.

So if I jump the relay socket to positive it should kick on right? Nothing. I even went to the connector on the clutch and no go, but it is shooting off some sparks like its trying to. I setup a permanent bypass in the relay socket and decided to go fiddle with the clutch, I finally got it to engage after spinning it around a bunch and pushing it in(with the car off, mind you, I don't recommend anyone try to manually engage the clutch while the car is running").

This is where I am in the process right now, so my next step is to probably check the wire to the clutch, the ground and I'm not sure what after that, will probably pull the whole the thing off and see if i can replace/clean the clutch without disconnecting any AC lines. I'm not sure if anything is bad inside since I've never witnessed the clutch engaged while the car was running yet. The resistance through the coil seems to be within spec, about 3 ohms, so maybe there just dirt in there and its not allowed to slide freely.

 

Update: It is definitely the clutch armature itself. The field coil and circuit path to the coil is good. The ground wires are clean, and everything to the motor and chassis are grounded. AC temp sensor is within spec, everything looks fine as far as I can tell.

I checked just for the hell of it, and the computer is sending the on signal to the relay. the load side of the relay has a line that is hot at all times. The other wire goes to the AC compressor clutch. One of the wires on the signal side of the relay is hot when ignition is on, and the other side is a line that the ecm pulls to ground when it wants to turn the AC on, when it wants to turn it off, that line basically get disconnected inside the ecm, and is an open circuit, tho I was getting some readings on the ohm meter when it was supposed to be off.

In any case, I can see what is happening to the clutch, it seems to be slightly seized up and thus wont pull into the pulley when its supposed to. One side was free enough to engage partly. That side tries to work no mater what position the clutch is in, so I'd say its not a dead spot on the field coil. The armature has a clutch plate on springs, that moves independently of the armature, but for the most part it looks like one solid unit.

I'm going to take a guess and say this car has been sitting for some time, or at least that AC was not used for quite some time. Here in Oregon, rust and corrosion are serious players.

 

My fix for this problem ended up being a 2 part solution. The first was soaking the entire unit in penetrating oil and then working the clutch plate back and forth with a small screwdriver. This did help free up two of the clutch springs but the third was still having some trouble, and needed some assistance.

The second thing I did was remove the spacer washer, with the washer in place, the air gap was somewhere around .03", which was within spec. Without the washer, my air gap became .015", which was .001" out of spec, (.016") but I was willing to give it a try just because its a free fix.

The alternative, and probably the proper way to do this, would be to replace the clutch assembly and field coil, but as far as this thread is concerned, the AC unit is fixed, it engages now, and doesn't rub when its disengaged, so I am happy.

This does somewhat confirm why the AC clutch was seized up though, it looks like there's another problem, low or improper refrigerant pressure, I can only get the clutch to engage when I bypass the pressure switch(and even when I do, I don't get cold air), so it sounds like it ran low on fluid, possibly leaking somewhere, and no one bothered to fix it for years, thus the AC clutch rusted up a bit.

Hope this helps any one having semi similar issues.