The present invention relates to compositions for use in refrigeration and air conditioning systems comprising 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone and at least one chlorocarbon, alcohol, ketone, ether, ester, N-(difluoromethyl)-N,N-dimethylamine, 1,1,1,2,2-pentafluoro-2-[(pentafluoroethyl)thio]ethane or mixtures thereof, and which are also useful in systems employing a centrifugal compressor. The compositions of the present invention may be azeotropic or near azeotropic and are useful in processes for producing refrigeration or heat or as heat transfer fluids.