This study developed a program for detecting charged refrigerant amount in system air-conditioner. System air-conditioner is an air-conditioning system with multiple indoor units. Due to the complexity of the system, it is more difficult to detect the refrigerant amount charged in system air-conditioner than in a general single air-conditioner. Experiments were performed for 6 HP outdoor units with 3 indoor units in a psychrometric calorimeter. The experimental amount of charged refrigerant was ranged from 60% to 140% with 10% increase. Fuzzy algorithm was employed for detecting the charged refrigerant amount in a system air-conditioner. The experimental data were used for curve fitting for general ranges for indoor and outdoor temperature conditions. Membership function were determined for whole ranges of experimentally measured data and rule-base were defined for each amount of refrigerant charge. Developed program successfully predicted the measured data within 10% resolution range.