I had the same thing happen to my Kenmore. It iced up/froze so bad
inside that there was no air circulating to the refrigerator. Once I
took off the back of the freezer compartment, from the inside, I could
see how badly it was frozed. Had to deice for 24 hours or longer to
get it to all melt. Then it was fine again for 6 months. Finally got
a new more efficient model.