I can only speak from personal experience but my conversion to 134 did not include a new expansion valve or dryer, only a complete flush and refill. It was done by a very reputable A/C shop that I have used several times before with great results. This past summer I drove up to Yosemite in really hot weather and found the the A/C worked as well as it ever did, no or very little change. Except for those in really hot climates I think the conversion is a great option. You'll likely be forced to do it sooner or later anyway.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

Irg, My last comments were not directed at the question of 134 versus 12 usage, rather to the advisablility of not using the expansion valve designed for the particular coolant, and replacing the reciever/dryer. If my system did not look like it would work with ONLY the normal flush,exp valve (mine is simply stuck) and new reciever dryer.... then I would convert to 134a for the advantages BillRok mentioned. I am concerned for the longivity of any systems which are opened up enough to have or need flushing and do not get a new reciever dryer installed..... it is only about $35 most of the time and in 30 years of reading about ac I have never seen a book or heard a professional indicate that replacing the reciever/dryer was optional.... That Silica type substance can only hold a certain amount of moisture.... then any excess is available for conversion to acid inside the system... Greg

Well, there are two sides to usual market theory... there does not need to be a scarcity of r12 if "People who need/want it" get scarce... which I think is what is happening now.

I don't know many who think 134 is a 'final' coolant.. just that right now it is the one the government makes it less hassle and cost to deal with...

Fortunately , we do not need to find a 100 year solution on our cars... rust will take care of their need for cooling anyway... and some MB's faster than others... ( sorry Edwardo )... but people will find a way to stay cool because that is the civilized way to exist ... , Greg

I had a few beers with an Indy last night. I asked him if he could work on my 76 and get the ac going. Answers as follows

1) F*** R-12, They want too much money for it, I have done almost 100 cars with r-134 and can usually get the vent temp down to 40deg F.
2) The York (piston) compressor uses oil only in the crancase and not in the system as the rotary compressors do.
3) If you re-build your hoses make sure they use nylon barrier hose. R-134 has smaller molecules and will slowly dissipate through the walls of the old material. But its OK because you can top off your system at home for six bucks a can.
4) On original refill use dye in the charge, then if you do devlolope a problem or leak it will be easier to find.
5) Its a good idea to replace your drier if you open the system.