If you're going to convert, you MUST change the oil in the system, as the two oils do NOT get along.
Typically folks change the receiver/dryer, expansion valve, adapter fittings, all o-rings in the ENTIRE system, compressor oil.
Thanks for the input guys. I'll definitely make sure to flush the system of the old oil and replace the seals. Does the dryer need to be fully replaced or can it just be flushed?I did exactly what Bilt4Me said. I flushed out the entire system using an A/C flush, replaced the dryer and replaced all the O-rings. I pulled the evap out to replace the expansion valve, flush it out, and get rid of 20 years of debris clogging up the fins. The O-ring kit I got had a replacement gasket for the compressor, so I flushed it out and replaced that gasket. Put on the R134a adapters. Put in the oil and buttoned the system all back together. I then pulled a vacuum using free rental pump from Autozone. Once I saw that it held a vacuum, I added the R134a.
It is pretty straight forward and easy. Oh, and I used Nylog Blue on all the O-rings and such because someone who was an A/C person on mud recommended it. It is one of the cheapest jobs I have ever done on the cruiser. I think I had maybe $50, including the oil and R134a.