As mentioned, first thing to do is replace all the fuses. Don't even look at the old ones, just throw them out. Don't even trust the color or rating of the fuse in each location, go by the sheet that tells you what color/rating fuse goes where. New fuses are kinda pricey at an MB dealer. Should be more reasonable at a VW dealer or a shop that caters to aircooled VWs. They're very cheap on-line (FastLane link above) but it'll take a few days to get them delivered.
Moparmike is right that the push-button units can get flaky but the typical case is flaky, not absolutely dead. With the engine running, switch between ACC modes. I take it the blower isn't blowing. Do you hear things moving behind the dash within 5 seconds of selecting a different mode?