2007 Scion Tc No AC and High Pitch Squeal

2007 Scion Tc, 150k Miles rebuilt title at 45k, replaced AC compressor at 85k with a salvaged compressor.

This is probably a stupid question, but I want to confirm it’s not anything else.

High pitch sound is coming from the pulleys (not sure which) when turning on the AC. AC does not blow cold air, not since the sound started.

I’m guessing it’s the compressor, can it be anything else?

I was planning on replacing the belt while I’m at it, anything else I should take care of?

I don’t have the equipment to discharge and recharge the AC myself, I was going to take the car in to do that, anything else I should know?
Any help is much appreciated.