In this study, effects of using HFO-1234yf and HFO-1234ze recommended as an alternative refrigerant on cycle performance and exergetic efficiency are presented. Because of HFO-1234yf and HFO-1234ze are suggested as alternatives of HFC-134a, the cycle performance and cycle exergetic efficiency parameters are presented comparatively for the refrigerants at the same working conditions and the same cycle. The effects of refrigerant changing process are discussed. It was concluded that from the results, the cycle performance and exergetic efficiency are almost same for HFC-134a and HFO-1234ze and higher than to HFO-1234yf. The difference between these values is 15% for 50 degrees C condensing temperature.