The heat/AC control on my 1999 Suburban will not operate correctly. It works at times only on high but does not push the air out up front like the rear air does. At times it(the fan) will stop completely . At random it will come on again. For awhile if you pushed the switch up or down or contorted it the(fan) would come on. That no longer helps. Is their a way of cleaning the contacts inside the switch unit or is it toast?