I need some help/advice on my Johnson controller. I have been using it to control my chest freezer for fermentation and lagering. I have the differential at 1 degree in an effort to keep control as tight as possible. In my most recent batch, I had it set for 51 degrees, and it never went over that, but would get down to 47 (using a thermowell). Is this much overshoot to be expected? Does the differential need to be changed? I am now heading down to lagering temps and have it set on 44 and am monitoring the air in the freezer now that fermentation is done. It has overshot down to 36 degrees. Thanks for your help!
It it dual stage (heat/cool)? I thought the JC’s were only single stage, which would result it what you have going on.
It is the A419 and it is a single stage. It is on a relatively new Kenmore 8.8 cu ft chest freezer. The only other thing could be that even though the differential is 1 degree, that when the controller shuts down power to the freezer at that point, there must be a whole lot more cooling going on. It might be a function of the efficiency of the freezer and not a problem with the controller, as it seems to be doing its job and turning the power on and off properly.
Yep, that’s the issue. It’s working properly for the cooling stage (50F set point will fire the freezer at 51F with a 1 degree differential) but then it’s going to cool until it reaches the freezer thermostat temp. I’ve seen dual stage controllers on eBay and eBay for around 50F. I have a two stage Ranco and my one degree differential will turn on the fridge at 51F and heating pad at 49F.
