AC Systems are fully sealed pressurised systems, if there not they don't work. Compressor failing? Bad luck, or the electromagnetic clutch has worn out, normally available separate. I've changed a fair few this year alone saving the customers a fair few quid, sometimes you can remove one of the spacers on the clutch and it'll work again for another few years. I did one today on a Volvo C70.
As for the VG on the Windows it does my head in, I clean my car weekly without fail and by the end of the week the inside of the Windows are disgusting.