Compressor capacity control of Air Conditioners has been considered as one of the methods for energy saving improvement.Unloader systems, pole change systems, and the like have been used for a long time, but recently air conditioner manufacturers have focused their attention on new air-conditioners with inverter-driven compressor systems. The EER & SEER of the latest type air conditioner will be more greatly affected by refrigeration system design than that of the conventional air conditioner.This report emphasizes saving energy, and analysis the factors for energy saving and their contributing ratio through experimental data. The results give design suggestions for an economically ideal, capacity modulated air conditioner.