To defrost my windshield I turn the dial that controls where the air is directed all of the way to the right that makes the air only come out of the windshield area and turn the temperature dial to red.. The AC button lights up. Is this the correct way? My friend says I am wrong and I should use the air direction button that shows the floorboard area and the windshield are and therefore the AC light does not come on. Which way is correct?