Frost going all the way around this box that covers the evaporator.

Hello
Found a GE side by side with duel evaporator, the problem is that it Is not cooling in the fresh food section. Upon taking out crispers noticed there is 3inches of frost going all the way around this box that covers the evaporator. This unit does not have a defrost system, what should we be looking for? We have not run into this issue before.
Thanks