I have the same problem with the fridge in my garage, soft ice-cream in the winter. There's nothing wrong with the defrost mode, it works fine 9 months of the year. Residential units are designed to be used in controlled temperature spaces.
I fixed mine by jumpering the door switch in the fridge compartment so the light is on all the time. I replaced the 60W bulb that came in the fridge with a 25W bulb. It adds just enough heat to make the fridge run more, and the freezer section stays colder now.
:):)
2001 Lance 1121 on a 2016 F450 โScuse me while I whinge.
And for all you Scooby-Doo and Yosemite Sam typesโฆโฆโฆ..Letโs Go Brandon!!!