[bowman1964]

well ok guys let me try to shed some real life info hands on i should say of converting a (lets say r12 to r134).now i have been buying and installing changeover systems ever since there was the new kid r134a out.now the compressors i have sold over the years( last 12 years i say) are made 134a but can easily be changed over with no problem to r12.we most of the time take the compressor and turn upside down and warm the unit alowing all the oil as possable to drain for a hour or so.now r12 doesnt like pag oil very well(r134oil)but it will with stand a small amount of mixing.now putting r134 in a r12 sysyem is the same way but the pag oil mixes alot easyer.pag oil is designed to allow for a small amount of mixing with minerial oil.now i sell orings for these systems and i will tell you there is no differance in the orings.
now i see you already know that removing water from the system with a good vacuum is a must.......but allowing a vacuum to stay on a system for too long will break down the oil in the system doing alot more harm than good.i usally run it for about 1 hour on a small system. 8 hours would be on a very large system.we service on the highway 18 wheelers people call them,,,road tractors .600hp diesels that haul everthing well all use everyday.these systems use 2.5 to 3 lbs of r134a.and we only vacuum them for a couple of hours at the most.these systems are 10 times the size of the systems we are building for a pc.i know alot of guys in here are very smart people and can read the specs on anything.but real the world sometimes is a little differant.i am not guesing or reading some elses stuff i have done it myself.i guess going on 20 years now.but i am not to old too learn.........that is why i come in here. one of the best forums on the internet and i am proud to be part of this fourm