A rubbing sound was observed from the compressor cooling fan
motor. Vibration readings were collected only from the motor as the fan is directly
mounted on the motor shaft. The obtained spectrum and waveform are given below.
An increased acceleration value in time signal indicates heavy impacts and asymmetrically shaped waveform (greater amplitude at positive
side compared to the negative side) indicates restriction in rotor movement
possibly created by rubbing. And also rubbing could happen only when there is
increased clearance in bearings.
The highest peak is observed at approx. 5.4X orders and its
harmonics also found in the spectrum. Since it is a non-synchronous peak, the possibility is bearing damage. Sidebands (sideband frequency is 18Hz, possibly
from a damaged ball passing cage) also present with raised noise floor,
confirming bearing damage.
Recommendations were provided to replace the bearings and
inspect motor armature. The bearings were found having play and damage. Minor rubbing observed on the armature, following which winding resistance and other electrical healthiness checks were performed, ensuring the satisfactory condition of the motor. The bearings were replaced and the motor was reused.
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