This 2000 Ford F350 with the 7.3 liter diesel engine came in with the complaint that the a/c works sometimes. It seemed to work okay when a cold engine was started but as the engine warmed up the a/c would stop cooling.
This one was easy enough to diagnose just by looking at the air gap at the compressor clutch hub. Normally the gap should be in the .015″ to .025″. This one had a gap of about .050″. A test that can be done is to run the engine with the a/c on and the blower set to the lowest position. Windows up and doors closed. Keep the engine speed between 1500 and 2000 rpms for a few minutes. Then let the engine idle for an extended period of time until the a/c starts cycling off and then back on. Check in on the operation until the a/c fails to cycle back on. Using a wooden broom handle or similar device, tap the clutch hub to see if it will engage. If it does you have just proven that the air gap is the problem. Be careful when doing this so that you do not cause harm to yourself, others or your vehicle. If you have any doubts about it do not do it!
In order to correct the air gap, the clutch hub will need to be held with a tool similar to the one in the next picture.
Then using a small ratchet and socket loosen the 8 mm headed bolt.
Finish removing the bolt from the compressor.
Then realize that you should have already removed the coolant tank to make life easier. It does have to be moved to slide the clutch hub off. There are two bolts that hold it in place.
A little gentle wiggling and the clutch hub should slide off of the shaft. Be on the look out for the shim. It may stick to the shaft, stick in the hub or just fall off.
This one had stuck in the tube in the clutch hub. A small screw driver was used to pull it out. Since the shim was about the thickness of the excessive gap, I did not install another shim.
I installed the clutch hub, without a shim, and checked the clearances and it was within an acceptable range. I installed the retaining bolt and mounted the coolant reservoir tank back into position.
Another one fixed. Obviously the better fix would have been to install a new clutch assembly and or a new compressor assembly.