Strange climate control
 

My 2013 ML550. Climate control set on "auto" just started being noisy (air flow noise, not mechanical noise). Switching out of auto reveals it's using floor vents, face vents, and defroster vents on auto. If I manually select just floor or face vents (or both), it's quiet. Any idea why it would start using the defroster vents on auto?

Did you get the extra option for rear seat climate control? I noticed mine included a mysterious "mist sensor" as part of that package (581), which I'm guessing can automatically detect that the window has fogged up and turn on the defroster.

I haven't had a chance to see if it works though - Colorado is a pretty dry climate and my ML parks in a garage, so I never really have an issue with misted over windows that occurs quite frequently elsewhere.

You've got a big car, and when it starts up, the sensors say you've got to replace all the air with fresh heated or cooled air. To do that it goes to full fan speed regardless of the setting. After a while as things stabilise, it will settle down to a moderate speed and you are comfortable.

The ML is no where near as noisy as some cars. Ear muffs are required in the Range Rover.

Regardless I usually reduce the fan speed which turns off the auto, and it all works fine albiet one minute later.

We are assuming the 3 airflow locations because that's what displays first. I wouldn't say that's my experience. I have never had the fans speed start in high even when the temp setting is full high or low. Each country surely has different systems of the same general layout. The electric heat in Canada sure is welcome. Not sure if Northern US can get it.

Did you figure out what the problem was? I have a noise that is loud when the heater is blowing hard and the A/C button is on (it comes on when I use the 'auto' feature). When I turn off the a/c feature, it stops immediately and starts again when you turn the a/c feature on. I remember reading a post saying the fans aren't syncronized, but I can't find it now.