Years ago, directing blower air onto the windshield didn’t automatically activate the air conditioner. Every car I’ve owned or driven recently turns the AC on in any air-flow position that includes the windshield.
For demisting inside the car, this is sort of OK. But it does force fuel-wasting AC use when a gentle stream of slightly warm air will keep the glass clear, which is most of the time.
For deicing, it’s just silly. I want max heat to melt external ice; pre-chilling the hot air - especially on startup, when the heater isn’t very hot - is a real problem. And in my last three cars, at least, AC does come on even when it’s below zero outside.
Any idea why this design choice was made? Are people really incapable of pressing two buttons when needed? And is there any way to decouple the two functions without doing something that would void the warranty? I’m guessing that it’s a hard-wired connection, or that one would have to take the dashboard apart to unplug a wire someplace.