Working on a Copeland R404a 5x7 walk-in cooler maintaining 15C/59F. Have been getting mixed advice on charging techniques. I normally charge to subcooling specs and 20-40dg compressor SH. Am confused about the 10-20dg TD charging rule and how to use it. I understand all freezers have a 10dg TD and Medium to High temp use 15-20 TD Can someone please explaine? Thanks in advance