On my 1991 300d, I was driving home tonight with the heat on in the eEconomy mode, and it was raining, so I got some fog on the inside of the windshield.

I turned on the down button to turn on the a/c compressor to get rid of the fog, but nothing was coming out of the dash vents. Then I realized it only comes out of the dash vents if cooling, from the floor if heat. At what temperature does it change? Seemed to be around 75 or so, but it's hard to tell. Either way, with the a/c compressor on, the fogging was reduced. I don't think there's any other way to keep fogging off the inside of the window (or does Rain-X make anything for the inside of windshields now?). You could turn on the defroster of course, but that's a band-aid solution.

Thanks,

jeff