R-23: Used in very low temperature refrigeration systems, typically on the low stage of a multi-stage system. Has properties similar to R-13 and can be used to replace R-13 in an existing system. R-23 has higher discharge temperatures than R-13, however, and equipment which is not designed to take this into account may suffer related failures. Polyolester (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.