As to wrong refrigerant (assuming it is still an R-12 system), I don't see how. The low pressure fitting (at the top, under blue cap) fits 134r hose fittings exactly. I had thought that R-12 fittings and 134 fittings were different and incompatible. I have no other clue as to retrofitting or not, since no one left a label of any sort.
What do you think? Thanks.