I haven a feeling your compressor is bad.

What is going on here, is the compressor is sticking when you turn the AC on. Once that clutch engages, and the pulley doesn't want to move. It will slow down everything attached to that compressor. In this case it's your crank. Your engine tries to stay running, and so the belt is going too slow, and gets dragged on by the crank pulley. There's your squeek. The motor is idling so low because that belt is trying to only let it spin as fast as the compressor can spin. Eventually that belt will break. You need to get a new AC compressor, and a new belt.