Abstract: Beat frequency noise from the air conditioner outdoor unit sounds discontinuous, the sound increases and decreases periodically, which negatively affects the users’ experience. In order to reduce the beat frequency noise, on the basis of spectrum analysis, it is found that the source of the noise is the quadruple frequency of compressor’s electromagnetic excitation and the quadruple frequency of compressor’s rotation work together. Further modal test shows that the natural frequency of reservoir is close to the quadruple frequency of compressor’s electromagnetic excitation, cause the reservoir amplifies the vibration of compressor. Change the connection mode between reservoir and compressor from clamp connection to welding, keep the natural frequency of reservoir away from the quadruple frequency of compressor’s electromagnetic excitation, the noise has been improved greatly.

Key words: Outdoor unit, Beat frequency noise, Modal analysis, Spectrum analysis