External thermal bypass for large coolers used in cold climates (32 degree -). Installs in cooler line. Includes bypass only! Use on 5/16" & 3/8" line sizes ONLY!! Opens fully at approx. 180 +-. This by pass is included in the Tru-Cool 4739 cooler. Add to the 47391 or any other cooler with 3/8" or 5/16" line. / 708-4739P6 /