The solar thermal cooling system at University of Indonesia is a cooling system uses mixed input energy between solar energy and gas. This system uses a single-double effect absorption chiller with cooling capacity of 239 kW. The solar energy is absorbed by evacuated tubular solar collectors in an area of 181.04 m2. The performance of this system is influenced by hot water that supplied from solar collectors. Solar radiation is unstable during the day because the weather condition and it should be anticipated with a corresponding the hot water flow rate. Hence this study focus on the variations of hot water flow rates, where the experiment is conducted with the flow rate of 8.6 m3/h and 12.1 m3/h. Finally, the performance and characteristics of this system can be shown in this study.