Bosch engine coolant fan motor - fault, disassembly, and failure analysis.

Friday, 4 Dec 2020
Fault:
The Bosch engine coolant fan motor (i.e., auxiliary fan) sometimes will only
start when it is nudged; once started, fan continues to operate normally.
Part #s:
Mercedes-Benz (000-500-60-93)
Bosch (0-130-701-229-INT)
Fault Analysis:
The Bosch motor has a start capacitor which provides electrical energy
for a very short (seconds long) period of time for motor starting.
The extra energy is needed to overcome the moment of inertia.
Once motor starts, electric energy is supplied via the brushes.
Without a capacitor, a flick on the shaft will make the single phase
motor run, provided the main winding is OK.
Things to check:
1. brushes - ok
2. armature (windings) - ok
3. start capacitor - faulty
1 & 2 ok because once motor is manually started it continues to run.
3 not ok because fails to start motor.