The results of azeotropic mixtures research with a normal boiling point between —40 °C and –80 °C are stated. The aims were to design refrigerants of the fourth generation and to match the saturated pressure-temperature characteristics and refrigerating capacity of existing refrigerants within this range. There have been selected three azeotropic mixtures R1270/161 (propene/fluoroethane), R170/717 (ethane/ammonia), and R600a/161 (isobutane/fluoroethane) of a large number of potential combinations, all formed from natural refrigerants or synthetic chemicals with a global warming potential GWP<150. Each of these has distinct characteristics and is suited to certain types of applications. Experimental measurements of P-T-x-properties were made for mixtures. Based on the results of the measurements, a thermodynamic model was developed using the Peng-Robinson type equation of state to predict the phase behaviour of the full range of compositions, pressures and temperatures. These new blends offer notable advantages over existing refrigerants, in particular: zero ODP and low GWP, below 150, and mainly «naturally» occurring fluids; improved thermodynamic properties (such as critical temperature and minimal temperature glide) over similar existing refrigerants; good solubility with oils; low toxicity, and reduced flammability; known and understood chemical and material compatibility.