2006 c6 z51
S/c paxton novi 1500
Cartek flip drive

So,
I bought the car and drove it for 3 days then I had to rebuild the motor.The a/c was working great before the motor took a sh*t.my car was at the shop for 7-8 months(that's another story.dont get me started on that)..I got it back and my a/c hasn't been the same.When it's cold it squeals like crazy,and when I turn it off everything's nice and sound.After getting on the highway and turning on the a/c it squeals for a little while then eventually goes away(still blowing cold air)...but then eventually stops blowing cold and starts blowing warm air...but this depends on how hot it is outside(I'm in south texas..100 degree heat in summer).Ive read a couple forums on here with similar problems...so here is what I'm guna try before replacing the compresser(Delphi),reciever drier,and orifice tube...

1.change out the belt that runs the compressor(I'm s/c with cartek flip drive.I have 3 separate belts)
2.try and recharge the system
3.sprinkle comet/Ajax on the belt to see if this helps any

The compressor/reciever drier/orifice tube has never been replaced.Im thinking it might be time..

Im not sure how to check the oil in the compressor to see if it's low or not..which this could be a reason why my a/c is having problems..

Any help would be greatly appreciated!