I've driven over 15 different Merc models for the past 8 months including my 19 C63s and different loaners such as 19-20 C class, E class, 19-20 GLC, 2020GLE, and I've noticed all have the same behavior on Air Circulation function whereas almost in all circumstances, it lets the bad smell inside the cabin when you pass a certain smelly area. I always have the fan and Air circulation as well as vent options set manually and I always leave the Air circulation option ON but for some reason, it keeps turning off when passing a smelly area. This has become very annoying and wonder if anyone has had the same issue here.

On my previous Beemers, I had this coded to set to previous selection and it would never change the value randomly.

AC systems in Mercedes are designed to turn off re-circulation when necessary

All manufacturers do this but some will lie about it like our Lexus which leaves the indicator on even when intaking outside air

Best practice I've found is leave it as is normally and when in undesirable areas manually turn it on say it stays for awhile

Thanks @Xec I'm convinced now but I'll keep fighting lol I've always turned the Air recirculation button ON (on all my vehicles) to avoid entering bad smell on the freeway produced from diesel trucks (Yes, I don't like that smell!) as well as passing by some agricultural or smelly areas. Again, this has to do with fuel efficiency aka new regulations. Meaning that when the air recirculation is off or in open position, the outside air enters the cabin which reduces the usage of the AC. Oh well 😔

I leave it pulling outside air most of the time unless it's a really hot day outside or like you mentioned you drive through an area with a pungent odor. Usually the moment you hit the button, within few seconds the odor should go away. But yes there is no easy way to make it stick unless you do some coding I guess??

Most cars turn off recirculation after some time automatically (typically 15-20 mins). It gets turned off automatically when you turn on the defroster as well. It is also not recommended to turn this on for longer periods of driving during cold days to prevent humidity build up inside the car.

Sadly, that's how it is.

Oh no. Is there a reason why you prefer inside circulation all the time? Or is it just because you can't stand the stinky areas? You've gotta be careful man. If one of your passengers has a smelly bum, that smell will be permanently lodged inside your car and vents with the re-circulation ON all the time.

Watch out!

To my knowledge, most of the European cars have had ionization system and dual activated charcoal filters. I believe in good air quality and the fact ionization system generates negative ions by its electrification method and changing positive and neutral ions to negative and disinfects and diminishes bad smell in the cabin while it gives you healthier, energizing feeling, and makes you aware.

Luckily, I never had any passengers with smelly bum (lol) except one time giving ride to a dude with smelly cloths and I had to go full AC blast and open the sunroof to survive lol

My brother has a 2017 C43 AMG (best sounding car btw) with purification and ionization package which he’s able to turn those options ON under infotainment system but apparently that option is no longer available for 2019+ U.S. cars while I can still see it under DE configurator… Not sure if we still have the ionizer in our cars.

I have a 2017 C43 and am not familiar with the two options you are referring to. Would you mind telling me where in the Vehicle settings these exist?

sure. Hope this helps: (watch from 0:50)

Thanks. That explains it. The Air Balance package is not on my car.

question to climate and a/c...do the car lose some power when Climate or a/c is on?

I'm sure it does slightly. This was very noticeable on older cars and would make a significant performance behavior. I remember turning OFF the AC when racing or launching quickly lol

Ye, and i think That.
but only a/c off, or? The climate not?