If you own an S-class 1992 or later and live in the south-east U.S., you might or very possibly will have to replace the evaporator core for the air conditioning system to continue to work. The deal is they all corrode from the outside in, not the other way around as one may think. Mercedes says that it is because of microscopic mites that can digest the aluminum the core is made out of. Mercedes has since re-engineered the cores and dipped them in plastic on the ends and coated the core with a chemical to resist the bugs. It's expensive and time consuming. Trust this repair to the dealer or only the best of independent shops.