NOVELTY - Refrigerant mixture (M1) comprises blend 1: comprising 35-65 wt.% of pentafluoroethane (HFC-125); 20-55 wt.% of 1,1,1,2-tetrafluoroethane (HFC-134a); 5-25 wt.% of 1,1,1-trifluoroethane (HFC-143a); 1-5 wt.% of N-butane (R-600) and/or isopentane (R-601a); and 2-10 wt.% of 1,1,2,3,3,3-heptafluoropropane (HFC-227ea); or blend 2: 45-75 wt.% of HFC-125; 5-20 wt.% of HFC-134a; 10-40 wt.% of HFC-143a; 1-5 wt.% of R-600 and/or R-601a; and 2-10 wt.% of HFC-227ea.    USE - For producing refrigeration in a refrigeration system (claimed) in mineral oil systems.    ADVANTAGE - The refrigerant mixture is low cost, has low flammability and toxicity, has refrigerating capacity similar to the existing refrigerant, is compatible with the existing system and lubricant, and has the ability to resist fractionation into flammable components upon evaporation or leakage from the refrigeration system. The present refrigerant blends are nonflammable, nonozone depleting, and may be substituted for prior art refrigerant blends HCFC-22, R-407C, R-417A, R-402A, R-402B, R-404A, R-408A, R-502, and R-507A. A combination of components N-butane and/or isopentane are selected such that the percentage of the hydrocarbon component in the refrigerant blend does not appreciably change as refrigerant leaks out of the system, and therefore does not cause the hydrocarbon component of either the vapor or liquid phase to exceed the flammability limit.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) producing refrigeration in a refrigeration system designed for chlorodifluoromethane refrigerant, involving obtaining a predetermined amount of chlorodifluoromethane refrigerant; substituting for the predetermined amount, a mixture (M1) of blend 1, where HFC-227ea is 1-5 wt.%; and    (2) using a substitute refrigerant blend in a refrigeration system, involving obtaining a predetermined amount of refrigerants selected from R-502, R-404A, R-402A, R-402B, R-408A, R-407C, and R-507A; substituting for the predetermined amount of refrigerant, a mixture (M1) of blend 2.