M Klasse Defrost Problems Low Heat Output

I had a similar issue with my old Ford Focus, though it wasn't a Mercedes. The windshield fogging was terrible. Turned out the blend door actuator was faulty, causing issues with the ventilation system. Have you checked the heater core itself? Maybe it's partially blocked?

Heater core check is next on my list. Where exactly was the blend door actuator on your Focus? I'm trying to get a sense of accessibility and if it's a similar design.

On my Focus, the actuator was buried behind the dash, near the HVAC unit. A real pain to get to. Given the stored error points to air distribution, and you are experiencing low heating output, the flap might not be opening properly. I'd strongly suggest taking it to a workshop, the error memory points to a faulty component.

Thanks for the insights. It ended up being a corroded connector to the air distribution flap motor, like I suspected. I cleaned it up and all is good. Total cost was 95€.