A performance evaluation for a residential window air conditioning system with microchannel condensers has been performed. First, a series of wind-tunnel calorimeter tests were conducted for two different prototype microchannel heat exchangers. The measured heat transfer and pressure drop characteristics for the heat exchangers were then compared to calculated value for four conventional finned round-tube designs, which were obtained using a validated simulation model for identical air and refrigerant inlet conditions. Finally, two prototype microchannel condensers are installed in the system and system performance tests were conducted. System characteristics such as capacity, energy efficiency ratio, and suction and discharge pressures and temperatures are presented, and compared with those for the conventional system. Refrigerant charge requirements for a window air conditioner with a microchannel condenser can be decreased by 35 percent compared to the conventional baseline system. The condenser core volume and weight can be reduced by 55 and 35 percent, respectively.