A lot of people say that their AC system never gets as cold when they go to R-134. I don't have first hand experience with that issue, so I can't say for sure. I have also read that properly pressurized R-134 system will cool just as well (I may have read that on a site that sells ac equipment, so that might be biased). I used to have an '88 with R-12 OEM system and it would get the cab FREEZING. I'm going to be fixing my AC here soon and I'm going with R-134, I figure some cooling has got to be better than none. There might be a day in the future when you simply CANNOT use R-12 anymore, so I figure I'll go ahead and changeover now.