The physical and thermodynamic properties of R-134a approach those of R-12 closely enough to provide similar levels of performance in systems with evaporator temperatures of 20 F (-7 C )and above. For example, bith the isentropic discharge temperature and the horsepower required per ton of refrigeration are nearly the same for both refrigerants. Also with a saturation temperature of -15.08 F at strandard barometric pressure, evaporator temperatures af 0 F and below are practical without maintaining a vacuum pressure on the low pressure side of the system.