I have seen posts concerning changes required to make the A/c converted to R 134 work correctly. My 91 350 SDL is low on gas and must have a leak. One of the options is to cnvert it to R143 for economy's sake.

Seems there were comments about the high pressure fan switch or the fans? What exactly should I be certain the technician does for the conversion?

The fan switch in the drier should be red in color and the pressure switch in the drier should be the updated version with high pressure cut-out. It would be nice to have a new expansion valve for 134a but not a have to. A new drier would be needed as well as having the lines flushed. Be sure to blow out the fins of the condensor and radiator to clean out the road bebris and get max airflow for cooling.
Hope this helps,

------------------
MB Medic
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop

I have had to go to the dual aux fans to help with the condenser core efficiancy. Your car may already have them though, if so it should be no problem. Do have the expansion valve done also. It has a tighter setting than the r-12 valve.

------------------
Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Thanks, I already do have the dual aux fans. How can one determine the vintage of the pressure switch?

The 1991 models should have the latest versions of switches on the dryer. The switch for the fans should be red(with pigtail). The reason that it was suggested that replace them(switches) is that they will start leaking after conversion, if they aren't already leaking.