There are a lot of causes for no AC, so when my car had no AC I started with the easiest things to troubleshoot. The clutch consists of a coil, a free wheeling pulley driven y the serpentine belt, and a pressure plate mounted on the end of the compressor shaft. When the clutch coil energizes, the magnetic field it generates pulls the pressure plate against the pulley, the plate then spins with the belt driven pulley, turning the compressor. When the clutch disengages, coil releases the plate and the pulley spins free, no longer turning the compressor. it is a strong magnetic force, when the clutch engages it does so enthusiastically with a loud sharp clack. Here is how I verified my AC clutch wasn't working.
1. With the car not running, key not in the ignition, battery connected as normal.
2. Reach in and make sure that the plate on the end of the compressor could turn. The pulley is locked in by the friction of the belt, but when the clutch is not engaged the plate on the end should still be able to turn.
3. I pulled the AC clutch relay. Luckily it is in the easy to access underhood fuse block
4. I used a voltmeter to verify that I was in fact getting 12V at the relay contact that gets 12V from the fuse. This wasn't necessary to test the clutch relay, but if I wasn't getting 12V there, maybe my problem was the AC clutch fuse in the awful to access under dash fuse block. (I had actually checked the fuse before moving on to the relay)
5. I used a piece of wire to connect the battery positive terminal to the relay contact in the picture marked as 12V to clutch. If the clutch was working, then I would be able to hear a loud clack when the clutch engaged. On mine, before the swap, I heard no clack. After the fix, the clack was unmistakable. It's a single wire running from that relay contact to the clutch, no other circuitry involved that might keep the 12V form getting there. The clutch gets ground from connection to the engine block.
6. After the fix, when I did get the clack, I left the clutch energized and verified that I could no longer turn the plate on the end of the compressor. It was grabbing the pulley tightly.
Here is a picture showing the location of the AC clutch relay, with an insert of the relay removed to show two contacts I mentioned above
- ACclutchRelay.jpg (68.52 KiB) Viewed 46272 times