This paper discusses the vibration characteristics of a fan discharge grille system, used in residential air-conditioning units, which has annoying rattles and visible vibrations. Three main sources associated with these rattles and vibrations were identified. These sources were the three common driving forces in the air-conditioning systems plus the excessive system responses to them. The primary causes for the annoying rattles were the torsional vibration modes of the grille driven by the fan motor torque pulsation at two times line frequency. Different experimental techniques--operation test, sweep test, impact test, and torsional shaker test--were used in the investigation. The driving forces could be identified by correlating vibration peaks in the operation and sweep tests with the fan rotating speed, blade passage frequency, and line frequency. The impact test and torsional shaker test without the fan installed could be used to clarify the nature of the system responses.

Units: Dual