Our Norcold has a defrost cycle in the refrigerator part but not in the freezer. We had to defrost the freezer a couple of times per year.
From the Norcold Quick Start Guide
"Does your model have frost limiter?
Norcold N510 and N6, N8 and 1200
series refrigerators are designed to limit
frost build-up on the fresh food compartment’s
cooling fins. Periodically, a temperature
control system automatically adjusts
to remove most frost from the fins and the
water drains into a collection cup in back
of the unit. Heat generated by the cooling
system then evaporates the water."