The controls to change the direction of air flow (defrost, etc.) are not working, but only some of the time. A quick search in this forum leads me to suspect that it is either the mode control motor or the linkage to it.

When the controls work, the lights above the buttons light up. When the controls do not work, neither do the lights.

If this is correct - how do I tell which is the problem?

Does the fact that it is only happening some of the time suggest one or the other?

thanks!