A Honda accord car had just been refrigerating outside. When the air conditioner is turned on, the electromagnetic clutch of the compressor does not suck when it is absorbed by the electromagnetic clutch, and its idle speed is high and low (850r/min-1100r/min). The fan rotates normally, and the refrigeration is bad. Check the electromagnetic clutch circuit of the compressor, and the voltage is normal. After determining whether it is not a circuit fault, use the multipurpose meter (manifold pressure gauge) to measure the high and low voltage ports of the air conditioning system. As a result, the pressure at the high and low pressure ends is abnormal. With the change of idle speed, the pressure tends to fluctuate. After asking the driver, there was no such phenomenon before filling the refrigerant, so he suspected that it might be too much refrigerant. When a part of refrigerant is gradually absorbed, a small amount of bubbles can be observed in the observation mirror when the engine speed changes. When the speed is about 1700r/min, the bubbles disappear and the trouble is eliminated. When the refrigerant injection of the air conditioning system is too much, the flow performance of the refrigerant in the system will be reduced, the compressor work is abnormal, the cooling is bad, and the engine idle speed is unstable.