RAV4 2007, air conditioner turns on automatically when I turn the vent

into winshield position ? Why? It's not like otherToyota that I have, when I just need windshield to be clear with warm air (winter time), the A/C turns on automatically when you set vent button at windshield position, what does that for how to use it and when to use it? hwo to use the mod of warm air to clear windshield like other cars?
Thanks