Something is up with the clutch of the compressor. The gap could be too large. The clutch magnetic coil could be bad. The ground on the compressor may need cleaning.

That Philips head bolt can be removed and you can clean that ground wire. See red arrow in pic.

Then test the resistance the clutch coil. See attached pic. Those are the easiest items to try first.

Update
 

Didn't see the last post until after I changed out the compressor. No change with the replacement compressor. The compressor won't engage even with pressure switch jumpered. Also, now both fans run for engine cooling (with or without the AC switch on), but neither run when I press the AC switch. I'm wondering if it's a wiring issue. I'm at a complete and total loss, as usual :confused:

Something strange is going on with your car.

First of all, when you changed the compressor, how did you refill the system, since the compressor isn't working? Did you pull a vacuum on the system?

Haven't charged it yet. My dad has a vacuum pump I planned to use this weekend to do it. I just wanted to see if the compressor would engage, so I jumpered the pressure switch.

Air doesn't really compress like R134a does, so don't try that test again.

I would unplug the compressor just to be safe. You can jump that pressure switch and recheck that you have 12V going to the compressor electrical connector.

Once the compressor is under vacuum, then you can try to see if it engages.

I really appreciate the advice. I'll put a vacuum on the system this weekend and check it out. I'll also double check the voltage at the compressor and post what I find. Thanks again!

What was this reading?

Was the new compressor grounded? If you just put the wire on and grounded it (no belt on the compressor) just to see if the gap closed you should be fine.....no turning the compressor isn't "compressing" anything