The fan starting current is too large.

The airflow in the air duct in the casing of centrifugal fan is actually the research field of fluid mechanics (resistance). Closing the air door can quickly form and achieve the required internal and external pressure difference (easy to inhale), and the motor impeller is unloaded in the closed flow channel, and the air resistance does not increase. If, after the air door is opened, the resistance of the impeller in the fixed flow passage increases with the increase of air intake (the starting speed of the motor is gradually accelerated), this is usually called starting with load, which will make the starting current of the motor too large and damage the equipment.