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.