It's a Hyundai safety feature for the automatic AC/Heating system. You can't disable it. Once you turn off the AC/Heater, it will remain on outside air only.
On my last car you couldn't use it together with the heater. Only on AC. So I didn't have to deal with steamy windows in the winter because I use only the heater then. Never had issues with stale air either. I use it all the time because most of the older cars in my country don't have catalytic converters and they smoke everyone behind them. A lot use LPG systems as well which smells if not properly maintained (almost all aren't). The downsides of living in a big city without properly enforced car-related laws I guess.Also depends on what cabin filter the car has. My Fiesta's cabin filter was a joke. However the filter on my Infiniti Q50 is amazing (and expensive as f*ck). One of the first things I'll do to my N when it arrives next month is upgrade the cabin filter (if better ones are available for it).
