What does the a/c compressor clutch do?
 

I was replacing my engine mounts today and I had to move my a/c compressor to get at the mount on the right side. When I did, I found that the single wire coming out of the compressor clutch is disconnected. I bought the car over the winter so I haven't tried to use the a/c yet. What does this wire do? Should I just plug it back in? Is there a reason for it to have been disconnected?

Thanks for the help,
Sean

it acts as a magnetic couple to your ac compressor when its switch on it engages your pump

Sean,
It may have been disconnected to make sure that the compressor wasn't accidentally activated by the AC switch inside as your system may not be charged or in good working order. Of course, removing the V-belt would also guarantee the AC didn't turn on. If you have any doubt it would be a good idea to take it to a garage to see if the system holds a charge (ie doesn't leak) before you allow the compressor to turn.

Could be the system is flat or the relay could be sticking allowing constant power to the compressor.

You can perform a quick check to see if the magnetic clutch is working. Just remove the V-belt (if its installed) and spin the AC pulley. It should be free wheeling. Then go into the car and turn the AC fan knob to any position above "0". You should hear the blower come on (with the igntion on). Go back to the AC compressor and now the pulley should be "locked" and turn the compressor. You don't have to actually start the car to do this. If all checks out OK just get the system inspected and recharged.

To make it simple, the compressor pulley normally spins freely. When the clutch is engaged, the pulley locks to the shaft and actually turns/runs the compressor.

If it's an original York compressor ('71 or '82), hook up the wire and see if the compressor works.

They didn't have a high/low pressure switch and will run even without freon. Won't hurt it for just a minute or so.