Not sure which fridge model you have but if it's the Dometic 4 door model there is an automatic frost reduction cycle that activates after 60 hours of operation and lasts for 2 hours. This repeats every 48 hours. I imagine that is what causes the units temperature to increase.
In the manual it is suggested to turn the fridge on between 6 and 10 PM. We shut it off when refueling so once we set up camp we turn it off for a few seconds during the 6 to 10 time period to get back into the correct cycle time.
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