odd refrigerator issue, Dometic

the unit is a Dometic 2852, it has always worked, but at times it wont get cold.... it will get cooler, but not cold on gas or electric.

sometimes it will get cold and work as it should.

all testing has been done on gas, with shore power disconnected from the trailer, and also on shore power alone with the gas off.

this unit had the automatic temp control with the thermistor clipped on to the fins in the fridge compartment... I thought it may be faulty so I replace it with the "Articca" adjustable thermistor from www.snip-the-tip.com...

this upgrade made a HUGE difference in how cold it gets when it gets cold, but it still has its problem of only getting cold sometimes.
when it works, the new adjustable thermostat will allow the fridge compartment to maintain 20degrees when the rest of the trailer interior is 80degrees... so im certain the fridge still has some useful life, if I can only find the intermittent problem.

the flame burns perfect and works great when it works, but it seems to be a thermistor problem and I dont know how the electrics work on these units or how the thermistor wires connect to the control panel, or if the board they connect to is bad, or where else the issue could be hiding.

im looking for suggestion as to how to further test it in an attempt to find the problem, or get it to fail permanently so that the local tech can find it.

thanks for any help you can offer..