The fourth one controls recirculate, and it allowed you to set in-between positions between 100% recirculate and 100% fresh air.
To simultaneously optimize pollution/humidity/CO2 I find I prefer about 80% recirculate and 20% fresh air, but achieving this configuration is impossible in most (all?) modern cars.
That's the workaround I'm forced to use, but obviously the disadvantages are noise exposure and forgetting it's cracked resulting in rain entering the car. :-(
Yay for "progress" eh? I know the recirculate door servo can stop halfway, just let me control it...
I used to do it in my former Skoda Fabia and the window just collapsed. Thank Indian roads. I noticed there is a subtle final movement from "cracked" to closed and I guess there is a big difference in vibrations related wear.
Toyota ran ads encouraging owners to crack windows in the rain and I noticed no final movement. But I'm not risking it.
https://i.ytimg.com/vi/W9AjhGko2mA/maxresdefault.jpg
The fourth one controls recirculate, and it allowed you to set in-between positions between 100% recirculate and 100% fresh air.
To simultaneously optimize pollution/humidity/CO2 I find I prefer about 80% recirculate and 20% fresh air, but achieving this configuration is impossible in most (all?) modern cars.