PLATINUM, SOUNDS LIKE A VACUMN LEAK AT THE SWITCH OR UNDER THE DASH. BLOWING OUT THE DEFROST IS THE MAIN CLUE, DEFROST IS THE DEFAULT SO YOU WILL ALWAYS BE ABLE TO CLEAR THE WINDSHEILD. HAVE TO HAVE GOOD VACUMN(AKA NO LEAKS) TO CHANGE THE HEATER TO VENTS OR FLOOR. AND YOU SHOULDN'T BE ABLE TO...