I have a problem with the temperature rise during compressor OFF cycle in a 20cu ft reach-in freezer. The system is R404A, capillary tube, heated glass door. The freezer reaches -20F, then the electronic controller turns off compressor, evaporator fan stays on. The controller differential is 10F, but the controller has a compressor minimum rest time 6 minutes. During those 6 minutes, the box temperature rises to about -3F to -2F. This temperature rise is excessive. I would like to see the box temperature not exceed -8F during the off cycle. The low side pressure is 9PSIG to 10PSIG, high side is around 240PSIG at -15F box temperature and 78F to 80F ambient. It looks that the greatest factor in this temperature rise is the warm refrigerant moving from the condenser to the evaporator. This refrigerant migration causes the evaporator coil to warm up, then the evaporator fan transfers the heat to the box. I was experimenting with the fan to have it cycle with the compressor, and yes the rise is slower during the off time, but, when the compressor and fan start, the box temperature jumps suddenly to about the same -2F or even slightly higher. I would like to avoid this option of cycling the evaporator fan for various reasons.
Has anyone experienced a similar problem - is there any way to correct this?
What temperature rise do you guys see on glass-door, reach-in freezers of this size?