Air conditioner Compressor cycling inconsistantly

My air conditioner compressor began cycling on and off constantly yesterday, but not at consistent intervals maybe two seconds on, five seconds off, ten seconds on, two seconds off, you get the idea. It makes a loud noise when it cycles back on and also feels like it "jerks" the truck when driving (for lack of a better description) when cycling back on.

My number one suspicion is that the compressor is seizing up, and the noise and "jerking" when driving is because the belt is pulling so hard to try to turn the compressor. (Please excuse my lack of knowledge of all the proper terms for what I am trying to describe hopefully it is coming across one way or the other!)

However, a part of me is hoping it still may "just" be something in the clutch itself or the pulley, or something off in the pressure due to low coolant.

The pulley is free-spinning fine when nothing is turned on to cause the compressor to try to run.

All I had time to do last evening was use my father-in-law's low-side gauge only (I know, I know); and it did read low, and I added some Freon. No change in cycling problem, but I know I need both gauges and a real Freon level/pressure check.

This evening I will have time and tools to check low and high sides and remove belt to check clutch and pulley assembly more thoroughly, so I just wanted to ask for advice on what to check for?
Should I even check those things at all or go straight for the compressor?
I have seen some things about compressor bearings, but confess to a complete lack of knowledge there and have not had time for research yet. Any help on that?

Thanks so much for any help I can get!