So we recently noticed that the freezer section of our refrigerator is not staying cold enough. It can GET cold (-5 F was the lowest that I read on the thermometer) but it does not stay cold, it creeps up to the +10 F range, and I got one reading at +15. I checked the airflow, and there is plenty of cold air blowing out and the seals around the doors are good. I'm looking for ideas on how to test and find that part that is not working.
Since it is blowing cold air, I am thinking either the thermostat or something in the defrost cycle, but I'm hoping for some help on narrowing the problem down.