I have a H.P. rack at 90* now.When it was first started up ,we had the end bells at 35*.Rack ran great. Then the store's refrigeration consultant came through and was whining about the ice on the suction lines.He wanted it all gone. We tried to tell him that ice is a good thing.....well he got his way.Thursday the D.C. started tripping. I found a 4D with a bad plate gasket.
Don't forget that high SH doesn't just cause high discharge temp, but also might cause the motor to overheat and trip. The Copeland envelope is based on 65F RG. At -25, 90F SH is right on the edge. There is no good reason to run more than 50-60F SH on a low temp rack, and at those temps you will likely see frost...but no liquid. Frost is not the enemy.