Often cause "24V DC Cooling Fan" fan does not turn causes problems are poorly maintained. If the power is turned off manually toggle stiff blades rotate, you should use some lubricant drip shaft, it can be lubricated, it will not affect the motivation to drag blades. Against wear and tear caused by "24V DC Cooling Fan" fan does not rotate, the easiest thing is to replace the parts, especially bushings, wear easily if burned.
If the capacitance decreases causing the fan does not turn, you can remove the "24V DC Cooling Fan" capacitors, the same model for a new capacitor is recommended to choose a large capacitance than the original 20%, there will be a better rotation effect.