A foam-like tube goes between the temperature sensor on your dashboard and the climate control unit. That tube usually deteriorates by the time the car gets to this age.

Remove the passenger side under-dash panel and look up in the direction of the temperature sensor. You will probably find that tube has literally fallen apart. Simply remove what is left and replace it. I did not bother looking for the correct replacement but simply used a piece ofr plastic tubing. Works fine and regulates temperature. The correct replacement may work better but I am satisfied with the plastic tube.