I got rid of my 95 Olds 98 last year. It was doing the same thing. My understanding after talking to a couple of mechanics is that the rubber in the Heating and Cooling controls switch goes bad and you loose controle of it all. You probably have the Dual controle so the passanger has his own controle knob.
About that time the CV joints started knocking and I just got rid of it. I was told it was $500 to fix the controls.