I have a 70 440 with factory ac. Rebuilt factory compressor seems to be seizing up. Belt is slipping and compressor is turning slowly when engaged. Has oil. I feel the problem occurred trying to charge the system by jumping the compressor. We had a problem charging and it probably ran too long without gas. It hasn't completely seized yet. Is there any way to fix the compressor at this point without a total rebuild? Any ideas appreciated

Oil for the factory compressor is in a sump, kinda like a V twin Harley. Doesn't really need gas to oil the compressor.

What are your pressures? Might be too much gas. You didn't dump liquid freon in to the low pressure side did you?

It's converted to 134a. It started doing this before we started to charge it

This in one of the things that is difficult to diagnose over a forum, but I have seen overcharged systems act the way you are describing. Were gauges used with the recharging. I usually will not jump the compressor, but will start a light recharge and let the system equalize until the compressor starts to engage, then continue with the recharge.

I am sure there will be some pros along shortly to add to your items to check.