A few years ago a Mr Goodwrench buddy of mine and I went through the '89 Suburban and converted it to R134. At the time Chevrolet was recommending a lot of new parts. I don't recall what all I bought, but we did it totally by the book. I seem to recall that a new condenser was the expensive piece. We had to totally evacuate the system and blow out all the lines too, because of some kind of incompatibility in the lubricants for the two types of systems.
Now my buddy tells me that GM has changed their tune and allows them to just evacuate the system, use some kind of dual purpose lubricant and shoot the R134 in there.
On the Suburban it was cheaper to fix the leak and upgrade the system than to shoot it full of R12 at whatever the price was at the time. We even replaced all the lines to the rear A/C from under the hood clear up to the rear unit itself.
I may have gotten a bigger condenser by going the expensive way, but I do not notice an appreciable difference in the cooling. I seem to recall spending something like $500 on the parts and freon, with a discount because my brother is a Chevy dealer.
