What was found
UPON TURNING THE COCKPIT DEFOG FAN TO LOW, SMOKE WAS OBSERVED COMING FROM THE DEFOG VENTS. SWITCH WAS RETURNED TO THE OFF POSITION AND THE CIRCUIT BREAKER FOR THE CABIN AIR SYS WAS PULLED. AN UNEVENTFUL LANDING WAS MADE. DURING REPAIR IT WAS NOTED THAT THE FRONT DEFOG BLOWER FAN BEARING HAD SEIZED AND THE INTERNAL WINDINGS OF THE MOTOR HAD CAUSED THE SMOKE. CIRCUIT BREAKER DID NOT TRIP. AFTER REVIEWING THE ELECTRICAL DIAGRAMS IT WAS NOTED THAT THE SYS IS DESIGNED TO COVER (4) 5 AMP MOTORS WHEN OPTIONAL SB21-8 IS INSTALLED. SB21-8 IS NOT ACCOMPLISHED IN THIS ACFT. ONLY (2EA) 5 AMP MOTORS ARE USED IN THIS INSTALLATION AND THE CIRCUIT IS PROTECTED BY A 20 AMP CIRCUIT BREAKER. THIS BREAKER SHOULD BE A MAXIMUM OF A 10 AMP BREAKER.