Why does my air/heat only work at the highest setting?

Replace your fan resistor module located behind glove box. Same happened to me. Eventually the fan won't work at all. After some months, my blower motor stopped. I just replaced it today. I have an extra resistor. I'll sell it to you for $12.00 if you want. It's brand new. I bought a second one because mine stopped again. I was hoping it was the resistor again, but it turned out to be the blower motor. Bought at Auto Zone for $103.00. If you buy your own resistor, you should be able to buy $15 to $25. DO NOT get at a Chrysler dealer!! They will rape you on the part and labor.