Geo Metro AC clutch slips on engage

1996 Geo Metro 1.0 AC clutch slips on engage for just an instant and than works and cools fine. Seemed to get worse after I added some R134. It wasn't cooling enough and had bubbles in the site glass. Now I get 40 degrees from the vents Slips longer in hotter weather when first turned on. It makes a metalic squeel. I don't think it sounds like the belt slipping. How can I tell if its the clutch or the compressor is trying to lock up.