PAG oils

Poly Alkylene Glycol oils - or PAG oils - were the first oils developed for use with HFC refrigerants and are perfectly miscible with these products, however they are very hygroscopic.  PAG oils are mainly used in copper-less air conditioning systems using R134a, because of their tendency to absorb water and their incompatibility with copper.  Being perfectly miscible with ammonia, PAG oils were adopted in refrigeration systems using this refrigerant.