Dual Climate Control problem

I am having an occasional "glitch" with my left climate control. I'll have it set on cool, but after 10-15 minutes of driving, it goes to full hot without moving the slide bar. The right side remains cool or wherever I have it set at. Usually after turning off the key and letting it set for a few, it begins working correctly again.
Anyone ever have this happen? Is the normal position of the damper door open when is has no power? (eg: the default position) I'm trying to figure out if it's the reostat or the damper door motor.
Anyone ever seen an electrical schematic for this circuit on-line anywhere?
Thanks, JW