R513A contains 56% R1234yf (an HFO) and 44% R134a by weight. At this ratio the two components form an azeotrope; the blend evaporates at a single temperature like a pure substance. R1234yf on its own is mildly flammable, but when it is mixed with R134a at this ratio the resulting refrigerant is non-flammable and falls into class A1. It can therefore be used in machinery rooms and equipment designed for R134a without additional safety measures. It boils at −29 °C at atmospheric pressure.
Its GWP is 631; less than half of R134a’s value of 1,430. Its pressures are about 10% higher than those of R134a: 2.2 bar g at 0 °C (1.9 bar g with R134a) and about 9.7 bar g at 40 °C. Its cooling capacity is equal to that of R134a or a few points above it, its efficiency is almost the same and its discharge temperature is slightly lower. Thanks to this closeness, in a retrofit the compressor, the oil and mostly the expansion valve stay in place; only the superheat setting is checked.
Its field of use is the same as that of R134a: chillers, milk and beverage cooling, positive-temperature cold rooms and cabinets, heat pumps. It is also common in the upper stage of cascade systems, in the circuit that takes the condensing heat of CO₂ (R744). When the evaporating temperature falls below −20 °C the suction pressure approaches atmospheric pressure and capacity falls sharply; that is why it is not suitable for frozen storage and blast freezing, and those jobs are left to other refrigerants.
In a retrofit the R134a is recovered, the filter drier is replaced, the system is evacuated and R513A is charged; no top-up is made by mixing it with remaining R134a. Because it is an azeotrope it can be charged from the gas or the liquid phase; even so, the habit of liquid charging should be kept. The equipment label is updated for the new refrigerant and the operation is recorded. For some compressor models the manufacturer’s approval and capacity table should be checked separately. After the retrofit the pressures and superheat are measured to verify that the system is running in balance.