I appreciate the comments, all are great. The problem is this: the previous owner says it was converted two years ago to R134A. I cannot find documentation in the records, and need to service the A/C with freon. I don't want to mix freons. I need to know if there is a particular way, other than the fitting appearance, what freon is in it now.

If I had the choice, I would not convert. But I want to know what state it is in now. Any ideas on identifying what freon may be in it now???