To ensure normal operation of the air conditioning unit after startup, it must be ensured that the condenser heats up well. Otherwise, the condensing temperature and the corresponding condensing pressure will be too high, so that the chiller high pressure protection device will stop and even cause a failure. The cold water in the evaporator should be circulated. Otherwise, the temperature of the cold water will be too low, which will cause the cold water temperature protection device to act and stop. Because the evaporation temperature and the corresponding evaporation pressure are too low, the low pressure protection device of the chiller will stop and even cause a shutdown. Cold water in the evaporator freezes and damages the equipment.