When I had my new Carrier a/c-furnace installed last fall.....after the workers were finished, I found a new small black "O RING" lying on the ground outside near the new compressor. The installer had to 'charge' the new a/c.....did this o-ring come from the removable black cap that is on the compressor?......(the black cap that was removed when the a/c is first charged.) If this o-ring did come from this black screw on cap.......will I get leakage without this ring? I did not notice the ring until after the workers left.....I called them once and they did not return my call. Carrier a/c....model # 24ABC 636 A300 Note: the o-ring was found near the back right side of the a/c unit......near the black capped 'charge valve'. I say 'charge valve'.....or maybe it's called a fitting.....but the black cap screws off. Any suggestions/comments?