Honestly, there is very little troubleshooting to perform here. There is absolutely no temperature control whatsoever for the freezer portion of your fridge on any Norcold or Dometic. The temp control is
only for the fresh food portion of the fridge. Remember that the temperature differential between the freezer and fresh food compartments is an engineered calculation based upon the size and length of tubing between the two evaporators - nothing more, nothing less.
A simple rule of thumb on whether or not the thermistor is/has failed is simple. They either:
(A) fail completely and with certain models of Dometic units will run wide-open which causes frozen food in the fresh food compartment, or on other models will simply not fire the boiler at all. It's very model specific.
(
fail by having erroneous resistance readings being sent to the control board which can cause wild swinging temps in the fresh food compartment. e.g. Perhaps 32 degrees one day, 45 the next, back to 40 etc etc.
There is absolutely nothing wrong with the thermistor IF the freezer is able to keep frozen items frozen (perhaps even visible frost on the back wall of the freezer portion), the door seals are good, and the fresh food compartment is above 40 degrees. This is almost always a failed cooling unit - which has most likely failed due to either a blockage that has formed in the absorption system tubing OR a compromised unit that has/is leaked/leaking coolant to the atmosphere.
In
most cases failed cooling units are caused by a blockage formed over time by running the unit out of level and the coolant has coagulated somewhere in the tubing thus preventing coolant from making it to the fresh food evaporator in a continuous flow. After enough coolant pools up above the level of the blockage then it will finally make it back down to the absorber vessel and eventually back to the boiler to start the whole process over again. Not having
any moving parts these units are 100% reliant upon gravity for the coolant flow.
Second largest cause for a failed cooling unit is very limited seasonal use or short cycling which causes condensation to form under the insulation around the boiler area which then causes premature rusting of the tubing which then eventually leads to a crack or hole of some sort in the tubing thus allowing the coolant to vent to the atmosphere. Or worse, it fails when the unit is operating. Since the mixture is highly flammable you could have a fire if the conditions are right.