Heater knob

Had the same problem, but the fix is easy. After many months of Air Cond use in SC, we went to the hills of NC this weekend, and needed heat. Got none. Thanks to this board, I found the heater control valve is easy to get to on the firewall, under the hood, on the passenger side. VERY CAREFULLY, unbolt the one bolt hooking it to the firewall, and open the top cover with the three small phillips screws. You'll see the device is a water valve on the top, with rotation controlled by the motor on the bottom, via a shaft drive. Carefully lift off the shaft, and pull off TWO pieces of gear at the top. Note the position of the valve slot. Like any water valve that has not been operated for a long time, it will get stiff. Too stiff for the motor and worm gear. I used a big screwdriver in the valve slot, slowly turning it right and left. It will go all the way around. Keep going until it feels comfortably firm. (took me about six turns each way). Put it back together, and bingo! everything works fine! Lesson learned: Turn on the heat full blast at least once a week, even during the summer, to keep that valve freed up!