W212 heating issue - different temperatures from both sides

[DrNick]

On my 2014 E class, its started giving a higher temperature from the passenger side vent. Eg if i set 19 degrees it sends out hot air and the other side is then trying to send out cold air to compensate.
If I turn it down to say 17 then the passenger side sends out cooler air but then heats up again. SO there is some control it it doesn't seem to be happy. Same result if I don't switch to to 2 zone.
Anybody got any ideas -are their two temperature sensors? Is there something like the old duovalve that was a problem on the W210/211?

 

[Will]

There’s more than two temperature sensors. Worth a look in the passenger footwell near the cabin filter, there’s a sensor there that can become damaged/detached during servicing (replacing the cabin filter)

It may log a code on STAR if you have it plugged in also.