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It could be several things. The first thing we do in the shop is test the cooling unit and rule out any issues with that AND test the thermister to be sure it is working properly. I will get you a copy of the Service Manual for this as soon as I get to my shop and it tells you how to do the testing. You will need a small digital multimeter like you can find at most hardware stores. About $20 or so and easy to use. I can direct you in the testing. Give me about an hour.
Here is the manual link. Print this out so you have it. See the section on testing the thermister. Check that first and let me know if it is in range or not. Then we can go from there. http://www.fourwh.com/NewDometicRefrigeratorManual.pdf
Just checking back in here to see if you were able to track this down or do you still need some additional input from me here