Refrigeration working fluid compositions containing difluoroethane or pentafluoroethane and a polyolester lubricant

A refrigeration working fluid comprising about 5 to 55 parts by weight of a synthetic polyol ester lubricant and about 95 to 45 pans by weight of pentafluoroethane refrigerant, the ester having a viscosity can be of from about 8 est. to 130 est. at 40.degree. C. and the working fluid having a miscibility value of -20.degree. C. or less, said miscibility value being the highest temperature at which immiscibility occurs over the composition range of said working fluid, wherein said ester is prepared by reacting:

• (i) technical grade pentaerythritol, defined as containing 85 to 92% by weight monopentaerythritol, 14 to 7% by weight dipentaerythritol and up to 2% by weight tripentaerythritol, an acid mixture consisting of branched C.sub.7 to C.sub.10 alkyl monocarboxylic acids and linear C.sub.7 to C.sub.10 monocarboxylic acids, said acid mixture having an average effective carbon chain length less than 7.2 and containing at least 25 weight % of said branched acids and up to 75 weight % of said linear acids, or.
• (ii) trimethylolpropane or neopentyl glycol with an acid mixture consisting of branched C.sub.7 to C.sub.10 alkyl monocarboxylic acids and linear C.sub.7 to C.sub.10 alkyl monocarboxylic acids, said acid mixture having an average effective carbon chain length less than 8.0 and containing at least 25 weight % of said branched acids and up to 75 weight % of said linear acids.