[RodeWorthy]

The fans are controlled by a heat switch mounted on the evaporator fins at the top vent. A method of checking this switch is to remove it from the fins and carefully direct heat from a propane torch towards the flat surface. Do not put the flame directly on, or even close to, the device or near the vent opening. You do not want to burn the rig down. A safer way might be to use a hair dryer or heat gun if you can get one to it.

Some have removed that switch and added a manual switch so they can control the fans manually. At least you would know if they are running or not.

Your problem may not be the fans. The thermistor mounted on the fins inside can be bad or the circuit board may have failed. The thermistor is the "whatever you call it" that you have already discovered.

One indication that the thermistor is not working will be that the lower cabinet does not get cold enough but the freezer gets down to below zero F degrees. I had to have my sensor replaced and the normal temp in the freezer is 8-10 F and the lower cabinet stays in mid 30 degree range.
When it was failed the freezer was very cold (below 0) but the lower cabinet was above 40.

Hope this helps.