Klimfilt

Hi guys, i have ML 350 (w164) US version, but i drive it in Europe (if it mattres). Here it's winter and yesterday i go out with the car and after 10 km distance my car was already reached optimum operating temperature but i notice that it's cold inside (it was over night and temp. outside was -3 C.). I turned heater knob to max temp 84 F (or 28 C. it's the same) and max speed of blowing, but the air blowing inside wasn't verry hot. I drive like this over 50 km but no change and it was alomost warm inside it's not the best temperature for long distance. It blows warm air, but it shoudn't be like this when the knob is on 84 F set.
Any suggestions what it may be the problem? I've read something about duo vent.? I didn't check my car with SDS yet (i will do it ASAP) but in dashboard i don't see any error messages or CEL light.

P.S. My heater module is 2-zoned.

Maj. Dundee

It's either your Thermostat is partially stuck open or your Coolant Circulation Pump is not working.