Chest freezer runs almost non-stop.

Question

Freezer runs at least 20 hrs. out of 24. Temp is -5 (F) and can't be set any warmer.Apatch of ice has formed on the outside at the back about 6 in. square. and 1/2 in. thick.
Freezer sits 3 in. from the wall,condenser coils are clean, door seal appears to be soft and pliable with no cracks. Unit has been defrosted.