An experimental investigation designed to determine the part-load performance of an ammonia-water absorption water chiller is described. The steady-state and cyclic performance of the chiller were measured under controlled conditions in an environmental chamber. Two valves were installed in the chiller to separate high- and low-pressure regions during off times, and insulation was applied to the chiller components. By these measures, losses due to cyclic operation were reduced by over 50%, resulting in a 6 to 7% increase in the calculated seasonal performance factor for typical northern and southern climates .in the United States. The use of the valves eliminated the need of the "spindown" period, thereby reducing the consumption of parasitic electrical energy.