My 240 has no AC and the manual style climate control. I don't know if my problem is due to the fact that I am back in the pacific northwest where it's very moist or something else is going on. I can't imagine it would be as bad as it is just because of moisture in the air but anyway.
I have severe problems with my windshield fogging up if I turn the heat on at all when the car is cold. If I turn the fan on full blast I get mist comming out of the vents that smells musty. The air comming out will clear up, and eventually the window will defog, but it takes probably 20 minutes before I can turn the heat on without fogging the window up. I know I am at the mercey of the dew point but it doesn't seem like it should be as bad as it is. And I have never seen mist comming out of vents before. Any thoughts.

__________________

I would check the drain for the AC to make sure it is not blocked.

water might build up in the housing and cause this situation.

Also the air compressor should kick on to dry the air when on defrost mode.

Steve

__________________
85 300d in progress

I don't have AC.

__________________

Hate to ask this, but do you smell the sickly sweet odor of ethylene glycol? If so, it is likely the heater core or a water line nearby that is leaking. Even if you can't detect the smell, this could still be the problem. Possibly all cars have the drain lines, even without A/C, and the leaked water could be trapped there if they are clogged. Not sure about that last part, heater leak may not be able to get to where the A/C drains are?!?

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Mine fogs the window at first too, but only until the temp gauge starts to lift. Welcome to the North West

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Do you get mist comming out of the vents when they are on full blast?


Where is the heater core? And will I be able to see a leak? I don't seem to be loosing coolant, but then I haven't been driving the car that much either.

__________________

You would smell it if it was leaking.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine