I would suspect a BAD lo speed on the fan motor(overheating the windings). But, it is easy to replace the tstat. I doubt the upper board is at fault. I doubt a reset will fix this type problem. Resets for operation problems rarely do on Dometic CCC systems. A quick test is to swap the Lo and HI fan speed wires and see if the fan fails when putting it to HI Fan(which will energize the LO speed wiring on the motor). If it fails on LO Fan(indicating the motor will not run on hi fan continuously), then you look at the upper board or the tstat. Doug