This study presents a detailed model to analyze small air-conditioning systems. The proposed model has relaxed the constraint of the fixed suction superheat or fixed temperature at the evaporator that was often used in previous studies. Detailed simulations for each component, namely, the compressor, condenser, expansion device, and evaporator, are made. The ability of taking care of complex circuitry design for both condensers and evaporators is also implemented. Comparisons of system performance were made with the four air conditioners. The deviations of the capacity prediction are less than 4%. Simulations were also performed to investigate the influence of the number of circuits. It is shown that the multiple-circuit design outperformed that of one-circuit design. For the same number of circuits, the system performance is related to the refrigerant flow distribution in each circuit. The more uniform the refrigerant flow in the circuitry, the better the overall system performance.