In this study, the performance of a new refrigerant, R1234yf/R134a (with a ratio of 89:11, by mass), was measured as alternative to R134a in automotive air conditioning systems using micro-channel heat exchangers in cooling and heating modes. Test results show that the capacities of R1234yf/R134a and R134a are similar in cooling and heating modes. The COP of R1234yf/R134a was lower than that of R134a by 4-9% in cooling mode, while it was lower by 4-16% in heating mode. The average compressor discharge temperature of R1234yf/R134a was up to 10 degrees C lower than that of R134a in cooling and heating modes. By adding 11% R134a, R1234yf/R134a can be made virtually non-flammable. In addition, R1234yf/R134a has no ozone depletion potential, with a global warming potential of less than 150, thus meeting the requirement of European mobile air-conditioner directives. R1234yf/R134a can be used as an environment-friendly replacement for R134a in automotive air conditioning systems, with minor modifications. (C) 2017 Published by Elsevier Ltd.