The air conditioning motor is an important source of noise in the air conditioning system, especially for indoor units. The electromagnetic noise from the motor has a low frequency and a tone close to a single-frequency pure tone. By identifying the noise generated by the air conditioning motor, the working condition of the motor can be determined. There are various methods for identifying motor noise, and this article introduces a practical load replacement method. The causes of electromagnetic noise produced by air conditioning motors are diverse, and their characteristic frequencies are generally related to the power supply frequency. Using the simple load replacement method, it is possible to distinguish between abnormal vibrations caused by uneven magnetic fields and vibrations caused by excessive load.
For example, in a certain indoor air conditioning fan, there is a peak at 600Hz in the motor noise frequency. Since its frequency does not change with the motor speed, and the noise disappears when the power is cut off, it is determined to be electromagnetic noise from the motor. Electromagnetic noise is generally caused by poor electromagnetic design or abnormal electromagnetic vibration due to loose stator and rotor. To identify the source of electromagnetic noise, the load replacement method is used.
Factors affecting the load on the air conditioning fan include:
1. Blade weight;
2. The position where the blade's center of gravity is loaded on the motor shaft (for blades that are statically and dynamically balanced well, their center should fall on the geometric axis), i.e., the length of the cantilever.
After replacing the blades with the same weight, under the same speed conditions, the 600Hz electromagnetic noise from the motor completely disappeared. A comparison revealed that the original center of gravity was relatively forward, far from the front bearing of the motor, which extended the cantilever length of the motor shaft and increased the rotor eccentricity during motor rotation.
Motor faults are an important cause of noise in indoor air conditioning units. To fully identify the noise source of the motor, in addition to recognizing its characteristic frequency using conventional methods, for some faults with less obvious characteristic frequencies, it is necessary to combine acoustic theory with other identification methods. Generally, the following rules apply:
1. For the same motor, the higher the speed, the lower its characteristic frequency;
2. Excessive motor load (excessively long cantilever) can cause electromagnetic noise from the motor, with vibration frequencies possibly exceeding 500Hz.
Source: Beijing Gree Air Conditioning After-sales Service Phone; Beijing Gree Air Conditioning Repair [http://blog.163.com/geliktiao_2012/].