Interesting topic...
Had the same thing happen to my (non-diesel) 300E.
Hosed off engine one day and that afternoon, no A/C (compressor wouldn't cycle). All was well the next day until I drove in a heavy rainstorm and then again, no A/C.
Never happened again since. I'm reluctant to wash the engine again...well, at least not until the dog days of summer are over!
