DO YOU HAVE AN ICE MAKER.. Ice makers put warm water into the freezer (Warm that is in relation to the inside temp of the box) and some of this evaporates and then condenses out on the colder surfaces and frost happens.
I use ice cube trays,, Same thing.
I defrosted mine Thursday, Friday being pay/shopping day the fridge was basically empty already. Moved a few items to the aux freezer, stored fridge contents in "Coleman Cooler" (Ok so it's not a coleman, picnic cooler) and cold bag along with some blue ice,, Turned it off and let it thaw
Finally cleaned, turned back on and later, ,,, Refilled.