I have a summit 570 kegerator which does not get cold enough. I bought the Johnson A419 - saw reviews everyone swears by it. I hooked it up, set at 32°F, the display reads 43°F and does not come on. I do not think it is bypassing the factory thermostat in the fridge - do I need to bypass it, and if so, how?
It sounds like you could be right - if the existing fridge doesn't get cold enough, then the thermostat is opening (disconnecting the circuit) above your target temperature, so the unit doesn't get cold enough. I'm assuming you've looked for some adjustment on the thermostat - most fridges have these.
So, if you have connected the A419 to the mains socket of the freezer, then the built-in thermostat still still be in play and will shut off the fridge too soon.
This thread here talks about the temp sensor being covered in ice prematurely, which is the reason they don't get cold enough. The fix was to improve the door seal, since that was letting in moisture causing ice buildup on the sensor.
This thread gives instructions on how to bypass the thermostat:
And the reply: