A refrigeration working fluid comprising at least two components, of which at least one is a lubricant comprising at least one chain terminated dendritic or hyperbranched macromolecule and at least one is a refrigerant. The dendritic or hyperbranched macromolecule is composed of a monomeric or polymeric nucleus having at least one reactive epoxide, hydroxyl, carboxyl or anhydride group to which 1-100, preferably 1-20, generations of at least one monomeric or polymeric chain extender are added, which chain extender has at least one reactive hydroxyl group and at least one reactive carboxyl or is an inner ether of such a compound. A dendritic or hyperbranched macromolecule wherein terminal functions substantially are hydroxyl or carboxyl groups is yielded, which macromolecule completely or partially is chain terminated by at least one chain stopper being a saturated or unsaturated, linear or branched aliphatic carboxylic acid or anhydride or a saturated or unsaturated, linear or branched aliphatic alcohol or ether alcohol. The refrigerant comprises at least one halocarbon, such as a fluorocarbon or a chlorofluorocarbon.