Common Faults & Troubleshooting Fan not rotating / abnormal speed: Measure the fan motor inlet pressure and flow. If pressure is normal but the fan does not turn, it indicates internal motor wear. If pressure or flow is insufficient, check the fan pump, filter, and oil circuit. Variable-speed failure (constant high/low speed): Faulty solenoid valve or abnormal electronic control signal. This unit has an electronically controlled variable-speed fan; check the solenoid and