I'd also suggest sticking with R12. I have done so in my '92 300e and the a/c air from the vents is freezing on max setting.

I also have '94 E500 with new a/c evaporator, receiver dryer, seals, fresh recharge....and the a/c air from the vents does not appear to be as freezing cold on max setting vs. the '92 300e's.

-fad