On Sun, 03 May 2020 13:40:39 -0700, wrote:

So what should the hysteresis be? and suggestions?

If you can find the specs for the original thermostat, that would be a
good starting point.

I have retrofitted a digital thermostat to my kitchen fridge. After a
lot of googling and experimentation, I ended up with the "on"
temperature at +4 C, and the "off" temperature at -17 C or so. The
sensor is attached to the evaporator in the back of the fridge, so the
air will not reach -17 C, of course.

Your fridge will be different. You will have to experiment. The lower
temperature needs to be set quite precisely, since the temperature
drops quite quickly at first, but very slowly towards the end of the
cycle.

Also, remember that the cycle time will be faster with an empty
fridge, compared to when it is fully loaded.