If "Cross Flow Fan" vent smaller resistance greater resistance layer, the pipeline flow is small, so that the lower cross-flow fan of the job requirements, at low flow eccentric vortex effect is not obvious. But when the speed is high, the vent area is large, eccentric vortex and greater control within the cross-flow fan or inhaled gas can not be properly discharged, the test system is abnormal situation, cross-flow fan surge phenomenon occurs, and there is a surge period, which specific performance: (1) increase in noise. When "Cross Flow Fan" normal operation, the noise is relatively small. But when the surge phenomenon occurs when the internal cross-flow fan Seoul issued a dull hum, when the Seoul-pitched humming sound, the sound is relatively large; (2) increased vibration. When the "Cross Flow Fan" surging phenomenon occurs when the car power transmission belt significantly shake badly, the entire test device Jie obvious vibration phenomena; (3) reading difficulties.