Have you checked the placement of the temperature sensor on the cooling fins? It's held on by a friction clip and moving it up or down helps to regulate the temperature in the unit. It's not a likely fix but it's by far the cheapest thing to check.
You could also have an issue with the control board for the fridge. You'd need a tech to trouble shoot the board. Sometimes they have a spare board on hand to swap it out and see if that fixes the problem.
You may also have a blockage in the cooling pipes, if that is the case it will be an expensive repair as that will likely mean replacement of the entire cooling plant in the unit.
Mike Nancy and the fuzzies
Fulltiming since June 2004
Volvo 660 MH tow vehicle
2005 MS 38RL
2007 Saturn Ion "toad"
2010 Gold Wing "piggyback"