Many air conditioners use fan systems for heat exchange.Vibratory motion and noise in the air conditioner occur when the aerodynamic force of the rotating fan blades act on the cabinet of the air conditioner.We calculated the aerodynamic force using CFD software "PHOENICS" and compared with the aerodynamic pressure produced by the testing system.We found that the calculation results agree with experimental results.On the other hand,reaction force corresponding to the aerodynamic force occurs,and then the reaction force transmits to the motor-feet.Finally,these transmitted forces excite support-structure of the motor.We also calculated the reaction force,using the results of CFD analysis.It is clear that accuracy of CFD analysis is very important to obtain the reaction force.