The present invention relates to compositions for use in refrigeration and air-conditioning systems comprising 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane and at least one chlorocarbon, alcohol, ether, ester, N-(difluoromethyl)-N,N-dimethylamine, or mixtures thereof. Further, the present invention relates to compositions for use in refrigeration and air-conditioning systems employing a centrifugal compressor comprising 1,1,1,2,2,3,3,4,4-nonafluoro-4-methoxybutane and at least one chlorocarbon, alcohol, ether, ester, N-(difluoromethyl)-N,N-dimethylamine, or mixtures thereof. The compositions of the present invention may be azeotropic or near-azeotropic and are useful in processes for producing cooling or heat or as heat transfer fluids.