1995 C280 Windshield fogging, anyone has same problem?

[andy_1100]

Trying to figure out if I have a problem, before ripping the dash and the heater plenum off.
Observations:
1. if the weather is a bit wet or moisture in the air I get a lot of fogging on my windshield, door windows and rear window. I live on the West Coast, most of time it's rainy.
2. It clears if I run the A/c on auto or defrost
3. If I park the car after running A/c and I come back in 15 min or so, I get a blast of hot very moist air from vents
4. In the summer I haven't noticed any condensation dripping under the car when the A/c is running
5. I don't have a moldy smell

Checked:
1. I have no coolant leaks
2. I have no rain water laking into the car, it's dry under the carpets
3. I've replaced A/C drain tubes and didn't find any debree plugging them
4. The air filter is dry
5. Rain water collertor drains are clear (in front of the windshield)

Now that the temperature dropped below zero deg C it takes a while before I can drive, need to wait for the windshield to clear. I had cars with no A/C, all it took is to turn the heat on and crack the window.

It feels like the condensation is collected in the heater core plenum and it doesn't drain. Is it just a W202 specific or it's a problem, Did anyone had this problem?
Looking for some help before I rip the interior apart.

[andy_1100]

Last 2 days we had the temprerature drop below freezing, -2...-5 deg C. I turned off the A/C and run straight heat with a slightly open driver door window, no fogging anywhere.

Done some more reading, it all suggests that I have a moldy A/C