The present study describes thermodynamic modeling of a novel cycle of ejector as an expansion device - called modified ejector cycle (MEC) - on residential air conditioner (A/C) to further enhance the COP improvement on standard ejector cycle (SEC). The difference between the SEC and MEC is the separator, namely the SEC uses a separator that has an inlet and two outlets, whereas in modified ejector cycle (MEC), the separator has only an inlet and an outlet in the system. Due to its environmental friendliness of R290 (propane), it is used to replace R22 as a working fluid in the numerical. The modeling results on the residential air conditioner with cooling capacity of 2.5 kW using R290 as working fluid showed that the COP improvement of the MEC was 42.86% at the condenser temperature of 45°C.