Regulatory and voluntary actions are beginning to limit the direct global warming potential (GWP) of refrigerants used in many applications. A new class of fluids called unsaturated hydrofluoro-carbons or hydrofluoroolefins (olefin HFCs) has been developed to address this concern. These new fluids are being blended with existing HFCs to obtain lower GWP replacements or substitutes for today??s refrigerants. This paper provides an overall assessment of the application of R513A@ an azeotropic blend of R1234yf and R134a (56%wt/44%wt)@ as an alternative to R134a. R513A provides specific environmental and safety features of interest including: no impact to stratospheric ozone@ 56% reduction in GWP compared to R134a@ no significant secondary adverse environmental impacts@ low toxicity@ and non-flammability. This paper will review thermodynamic cycle performance and heat transfer characteristics of R513A relative to R134a. Material compatibility and chemical stability have been demonstrated to be favorable and test results will be compared to R134a.