R-508B:
Used in very-low-temperature refrigeration systems, typically the low stage of a multi-stage system. R-508B has properties similar to R-503 and can be used to replace either R-13 or R-503 in an existing system. The discharge temperature does not increase significantly compared to R-23. POE lubricants should be used, and it may still be necessary to charge hydrocarbon oil additives to ensure proper oil return. Check with OEM for specific oil and charging recommendations.