Abstract: During the commissioning of the thermostatic and humid static air conditioning unit（THACU）, four THACUs in MCR and computer room are turned on and off frequently, which will threaten the safety and life span of the units. Meanwhile, when the four THACUs are in operation, the heater is running at 100% power to keep the environment under a constant temperature, which causes a serious waste of electrical power. Through the alteration, the problems are solved and the THACUs can operate properly and stably.