Line of two-stage reciprocating compressors has been upgraded to include thermostatic expansion valves and can be operated with R448A and R449A refrigerants. With low global warming potential (GWP) values of 1386 and 1397, respectively, both refrigerants are ecologically friendly alternatives to R404A, whose GWP value is 3922. The EU F-gas Regulation prohibits the use of R404A beyond the year 2020 in stationary areas. Tests have shown that the technically improved compressors can be run with the two replacement refrigerants, both with and without a liquid subcooler.