Disclosed here in are refrigerant or heat transfer fluid compositions comprising C.sub.4F.sub.9OC.sub.2H.sub.5 compositions and at least one hydrofluoroether, which are useful in refrigerain or air conditioning apparatus or as heat transfer fluids. The compositions of the present invention are also useful in centrifugal compressor apparatus that employ two-stage compressors or single slab single pass heat exchangers.