This study deals with the launch time of main characteristic of NH3-H 2O absorption chiller under different working condition. The aim of this work was about to scrutinize a lumped-parameter dynamic simulation of aqua-ammonia absorption chiller in addition to investigating the effect of subcooled liquid at condenser/absorber outlet on absorption chiller’s key parameters launch time. Also, the effect of ambient temperature on absorption chiller’s key parameters’ launch time is studied. In order to determine the thermodynamic properties of the working fluid, the Engineering Equation Solver software is applied. By making a link between Engineering Equation Solver and MATLAB software, the differential equations are solved in the MATLAB software environment by fourth-order Rung–Kutta method. According to the result, increase of the sub-cool liquid temperature at condenser outlet has no effect on absorption chiller’s key parameters’ launch time. Besides, 10 ℃-increase in subcooled liquid temperature at the absorber outlet leads to decreasing the launch time of the coefficient of performance to 19.35%. The result shows that if cooling tower temperature goes from 22 ℃ to 30 ℃, launch time of the coefficient of performance rises by 10.43%, while evaporator heat transfer rate falls by 30%. To validate the dynamic model, the results deduced from numerical simulation are compared with peer steady–state results.