Vibration modes associated with a fan impeller, motor, and motor mounting assembly in small air-conditioning units can be excited by motor torque pulsations in single-phase motors. Experimental procedures were developed that can be used to measure the torsional resonance frequencies of the stationary parts (motor stator and motor mounting assembly) and the rotating parts (fan impeller and motor rotor and shaft assembly) of a propeller fan assembly. Impact test procedures, test procedures in which the fan motor is set up to act as a torsional shaker, and procedures that employ the use of a microphone in an anechoic room are presented in this paper.

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