I can't be for sure but sounds like what happened to me a few years ago. Mine would squeal and became louder when I hit the gas then one day it stopped working. I never checked it out until this year because I assumed it would be an expensive fix. My compressor went bad and from what I read the squealing is a sign of it on its way out. With a baby this year I figured I'd spend a little money a try to get it working. Bought a compressor off ebay from a guy who rebuilds them for about 80 shipped free, also bought an accumulator and orifice tube(but didnt put it in because looked like a pain and was told because it didn't blow up it wasn't absolutely necessary) Its possible that the compressor has a leak somewhere, I had no leaks anywhere else so basically my compressor failed. Fixed mine for around 150, compressor, accumulator, ac oil and some R34, pretty easy to do if that's whats happening with you. Oh and my dad was able to borrow a vacuum pump which is needed to draw a vac on the system.
