W124 What temp makes it come out of different vent?

[jbach36]

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

[speedy300Dturbo]

When the center button is depressed, enough air should come out from the defrost vents to prevent the windshield from fogging up, even with the blower speed on low. Maybe your defrost vacuum pods are bad? Fortunately, they can be replaced without removing the dash.

[dlssmith]

I usually hit the defrost for a minute or two to clear the moisture, then hit the center button to maintain constant humidity inside the cabin. If yours is working correctly that should do it.

[Rick76]

Rain-X does make a product for the inside of the windows called Anti-Fog. I bought some recently but haven't had a chance to apply it.

[Rusty Boltz]

Rick76--I would use caution with the antifog product in case the formulation has not changed from what I tried. Maybe you would be better off doing a small test patch in a little used portion of the windshield. I tried the stuff in my truck a few years ago and it did keep actual fog from forming. However, after a couple of weeks I began to notice a dirty film on the inside that I never got completely rid of. I threw the product away. The film would disappear in a spot if it was rubbed really hard with a towel or clean cloth. it would always reappear in a day or two and no glass cleaners I tried would get it to stay off. This was a pre air conditioning pickup and did not have an antifreeze leak in the cabin which can also make a film. It reminded me of Armour all protectant on the glass, but it was a steel dash and never saw Armour-all.

Just to be safe you may want to do a test patch.

[jbach36]

With any other car I've owned, Honda or Toyota, I simply hit the a/c button which turns on the compressor, then slide the temp control to wherever I want it. On the Mercedes, if I hit the a/c button (the stupid buttons with arrows on that are confusing to any normal person) I simply get cold air unless I put the temp wheel at a pretty hot temp, then it goes out the floor vents, not the dash vents. I was just wondering at what temp that it switches from dash to floor vent. Using the a/c button will control the fog but the a/c sucks a lot of power/speed from the 5 cylinder diesel.

Thanks for the FYI on the problem with the anti-fog stuff you used. I'll be careful. Using Rain-X on the outside is awesome; great stuff.

By the way, simply CLEANING the inside of your windshield with Windex or other generic cleaner really helps reduce fogging on the inside during warmer times of year. It can't prevent the normal fogging from warm inside to cold outside on a rainy day however, but it certainly helps a LOT during other times of year. Clean the inside of your windshield!

1991 300d, 95k