Energy saving is considered one of the important factors in the green and sustainable development strategy of universities. Air-conditioners are currently equipped in most large-scale universities. Managing diverse types of air conditioners in large quantities and flexible schedules creates a big challenge for the management departments. In this study, we present an approach to deploy an air-conditioner management system toward power saving and compatibility with room usage demand. Additionally, we also include blockchain technology into the proposed approach to improve privacy, security and transparency. The approach is implemented and evaluated practically at Thu Dau Mot University. The results show that the approach has significantly saved energy costs related to air-conditioners up to 45% as well as improved the privacy, security, and transparency of the system.