1. The actual fan RPM is 30% lower or higher than what is being called for.
2. Blown fuse.
1. - Vent/air intake lengths exceed the maximum allowed lengths.
- Check for obstruction or blockage in the vent/air intake pipes or at terminations.
- Check the wiring connections at the fan and at the main control board.
- Replace the fan.
- Replace the main control board.
2. Replace fuse F2 on the control board.