Abstract: In order to solve the abnormal noise problem of the whole machine in the frequency band of 196 Hz~208 Hz when the compressor operates at 94 Hz~104 Hz under heating condition of the outdoor unit of the air conditioner, firstly, test the vibration of key components of outdoor unit and preliminarily find out the components (pipelines) with high correlation with abnormal noise. Secondly, the modal analysis of the pipeline is carried out to find out the pipeline modal which is close to the abnormal noise frequency. Then, through the Operational Deflection Shape (ODS) of pipeline, the vibration form under abnormal noise frequency is obtained, and compared with the modal shapes of pipeline, so as to finally determine the location of pipeline abnormal points. Finally, appropriate counterweights, such as rubber rings and pipe clamps, are arranged at the position of abnormal points of the pipeline. The results show that fixing a 40 g rubber ring at the second bend of the exhaust pipe and a pipe clamp between the exhaust pipe and the large valve pipe can effectively control the abnormal low-frequency (196 Hz~208 Hz) noise, and the noise peak can be reduced by 20 dB, which provides a reference for the forward design of pipeline counterweight.

Key words: Air conditioner, Pipelines, Abnormal noise, Modal shapes, Operational Deflection Shape (ODS)