The Compressor Clutch could be slipping. That was my problem that I just fixed. I replaced the clutch without taking out the compressor. It was not that hard contrairy to previous posts in this forum. Total Cost $ 30.00.
To check the clutch: check the air gap, specification 0.014 inch to 0.033 inch.
If you have very cold air when your A/C is on, it is NOT your compressor.
For more info check out this forum:
http://www.autoacforum.com/ There are several auto a/c mechanics that are moderators.
Good luck,
Mario