2000 Galant a/c fix

Hey all -

I recently found a fix for my daughter's 2000 Galant 2.4L auto that has had intermittent a/c issues.

Symptoms:
When really hot outside (the time you REALLY want the a/c to work) the a/c was intermittent. I'm not talking about the typical nature of proper cycling with the a/c clutch; I'm saying that when it was really hot out, the a/c clutch would not energize at all. However, when only "warm" outside, it worked just fine. It has been this way for several years; it started before I bought the car from my friend, but they just tolerated it and never fixed it.

Suspicion:
I suspected that either a switch or relay was going bad, or maybe the clutch was going bad and dropping continuity when it got hot. The a/c charge pressure was fine; it was not low on refrigerant, and would work well when not under high heat condition. I was convinced it was electrical and not mechanical in nature.

Solution:
I traced the a/c signal from the pressure switch on the receiver all the way back through the circuit; everything was telling the clutch to engage, but it would not. The system works this way (and understand this is applicable to my car, but may not be true for other generations ...)
The clutch gets +12v supplied to it via the wire, but grounds through the body of the clutch. This is not unheard of, but has it's frailties. Other systems use a twin wire lead (both pos and neg in the wire harness). But this particular OEM system uses the clutch body for ground, so only the pos signal is sent via the wire. After many years of dirt, oil, grime, etc being present, the clutch body was actually losing contact; hence no ground to complete the path! The fix was simple; I had to restore the ground path.

I actually discovered this by accident. After assuring that the signal was going all the way to the clutch itself, I just assumed the clutch was the culprit. So I ordered a new one from AZ and had to wait a day for it to arrive locally. So I went about dis-assembly, to remove the old one in preparation for the new one. When I was taking it off the shaft (I had to use a puller, gently, after taking off the retaining snap rings), I notice a ton of film and grime present. I removed the clutch and checked it's continuity off the vehicle; it was fine. I realized that as the vehicle was getting hot, it was just enough to cause the clutch body to have intermittent contact. After cleaning up everything well (used a dremel and small wire brush), I put the old clutch back on and everything back together. After a month of really hot weather here, it's not failed once to engage. To be honest, I think it's a pizz-poor way to design it; they saved the cost of the second wire in a short harness. I would much prefer to have the full polarity of both wires. But the bottom line is that this system does work WHEN IT'S CLEAN ENOUGH TO ASSURE FULL CONTINUOUS CONTACT!

I'm not saying this remedy will always fix your a/c issues, but if you've assured yourself that the system is commanding the clutch to engage, yet it's not, you might try to save yourself some money and look for this failure mode before wasting cash.