In this study, 14 refrigerant mixtures composed of R32, R125, R134a, R143a, R152a, and R1270(Propylene) were tested in a breadboard heat pump in an attempt to replace R22 used in most of the residential air conditioners and heat pumps. The heat pump was of 1 ton capacity and water was employed as the secondary heat transfer fluids. All tests were conducted under ARI test A condition. Ternary mixtures composed of R32, R125, and R134a were shown to have 4∼5% higher COP and capacity than R22 and hence they seem to be very promising candidates to replace R22. On the other hand, ternary mixtures containing R125, R134a, and R152a have lower COP and capacity than R22. R32/R134a binary mixtures show a 7% increase in COP and have the similar capacity to that of R22 and hence they are also good candidates to replace R22. Special care must be exercised when a suction line heat exchanger is used with these mixtures in air conditioners. Finally, the compressor discharge temperatures of all mixtures tested were lower than those of R22 by 15.g∼34.7t, which indicates that these mixtures would offer better system reliability and longer life time than R22.