So at the beginning of the week I had a local shop do a couple of things on my '96 Dakota (V8). One of these was to replace the serpentine belt. Today was the first chance I had to really drive the truck and I noticed an odd noise that would kick in and out. When I got home I popped the hood and quickly realized it was coming from the AC compressor.

It appears to be (mostly) locked up, but not completely. If the heating system is turned on, it occasionally engages noisily and then stops spinning. If the heating system is turned off, the pulley doesn't spin at all, meaning the new belt is being dragged over it. Before I had the work done there were no noticeable noises and it was working fine, though I did notice that day I took it in that it took a while for the defrosters to work on a very cold morning after a few days of very cold temperatures. Still, it seems an odd coincidence and I would have expected the shop to notice that the pulley wasn't spinning after they changed the belt.

Any thoughts? Obviously replacing the compressor will have to happen, but it seems weird it moves at all but only when the heating system is engaged.

 

Probably bearings going in various places in the clutch/compressor. Replace it, and you should be golden.

 

Has anyone added freon to it? If overcharged, it will basically hydra-lock....
Personally, I would start with a set of gages and see what it does when it tries to start. Assuming pressure is not going real high or liquid freon is in the suction side, I would then take the belt loose and see if the compressor pulley is smooth.
After that, probably replace the compressor and associated parts and procedures.

 

Nobody has touched it since I got the truck six months ago. The AC worked fine the few times I used it during the summer.

At the moment it looks like I either was incorrect when I said the pulley had locked up or it has resolved itself. I fired the truck up this morning (its had no problem starting) and looked at the compressor more closely. I verified that the pulley is spinning freely, and its possible it was doing that yesterday as I did not verify my diagnosis of a lock by touch, but simply was going by sight. What I assume is the clutch is engaging and running noisily but is not making the same noise it was yesterday. As I said in my original post, we did have a few days of very cold weather last weekend, so I guess its possible that impacted the bearings and now with the warmer weather they are working again. At this point I guess I will just keep an eye on it.

 

There's a possible confusion here.

When the compressor is NOT engaged, the pulley spins on the bearings.

When the compressor IS engaged, the pulley is locked to the compressor; it doesn't actually spin on bearings anymore.

I'd get the refrigerant level checked ANYWAY.

RwP

 

If it is noisy while engaged, the compressor is failing. Time for a new one.

 

It probably is the compressor.... Unless you are capable of replacing it, and doing the other work needed, ie flush,: replace drier, evacuate, recharge, etc. I would let the shop doing the work diag. the problem.

Its possible it is something else, idler pulley, etc.

Considering summer is over, you may just unplug the compressor and run it for awhile and make sure the noise is AC related.