A blend of R-22 and R-218 with hydrocarbon R-290 (propane) added to improve oil return. Though this product was originally developed as a replacement for R-502, it has come to be used as an alternative for R-13B1 in single-stage, low-temperature systems.

The evaporator will operate in a vacuum when the low side temperature is below -55F. When existing R-13B1 systems are retrofit to R-403B the capillary tube must be replaced
with a longer/more restrictive size. Similar lubricants can be used for R-403B, with any additives the manufacturer may reccommend.