My 2000 Eldorado ETC won't switch on the right side from A/C to heat. I'll drive to work with the heat / defrost on and the left side will produce heat and clear windshield and the right will blow cold and the windshield will be covered with moisture on the outside fron the chilled glass attracting outside moisture. Thank God for the heated seat otherwise the hot on left and cold on right would be A wash!