As Jerry suggested...The switch itself is most likely the culprit. Pull the control panel off to check the back of the switch. The terminals on the back of the switch commonly melt due to the voltage sent to the switch. The wire will probally be melted also.
To remove the controls for inspection of the switch....
1. remove the ash tray....there is a philips screw behind it....remove the screw.
2. remove the defrost vent cover.."goes across the top of the dash" Pops straight up. To remove the cover use a flathead screwdriver to pry it up. It will pop right off.
3. You will see two philips screws holding the top of the center dash bezel after you remove the defrost vent cover ...remove the two screws.
4. pop the center dash bezel off....just grab it and pull...pops off after the screws are removed.
5. The heater/ac controls will be held in by 4 philips screws...remove them and pull the controls out.
6. Inspect it.
Very simple, really just a few screws.