a. Hold the "220V Cooling Fan" feel its vibration, and converting FLAC feel different angles are the same, the fan vibration well, if vibration may produce a total shock to the chassis, before some start-up sound very loud when people mainly produce shock caused when the fan starts.
b. should only hear the sound of the wind (Some may have high speed electromagnetic sound), if other sounds are instructions on their quality is not very good. If it is not, as seven centimeters high fan speed in DC "220V Cooling Fan" speed does not exceed 3500RPM, but the wind can explain the poor quality of their big fan!
c. hand to prevent its fan rotation (do not put the blade broke) a minute or so, touch "220V Cooling Fan" fan center feel its temperature, if the temperature is high, the failure so it can prevent the fan when stuck It was burned, causing a fire.