I tried the 134a conversion on my 300SD, but switched everything back to R12 once the compressor locked up. I wasn't really satisfied with the new freon in the older system anyways. We charge $39 a pound for R12 at the dealer versus $13 a pound for 134a, but I think that the old stuff is a world above the new stuff. Gets much colder in that old system (at least in the first generation climate control system--that is). Just my 2 cents.

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Rgds,
Aaron Greenberg
MB technician
'67 250SE Cabriolet
'77 450SL
'79 6.9
'79 6.9
'80 300SD
'85 380SE
'89 420SEL
'93 300E 2.8