I have converted 3 cars to 134A with great success. I would change the drier, expansion valve, o rings, and change the oil in the compressor. Depending on the age of the high pressure line, I would consider changing that as well. Some say that 134A does not get as cold as R12. I disagree, as long as you don't over charge. Only put in 80% of what your system holds. This can be done for under 100 bucks if you don't have to change any hoses.