I had some spare time (we are currently at Fundy NP Headquarters Campground, NB, Canada, heading for Nova Scotia) and checked the back openings of the fridge. The air deflector at the top is ok. Could be better. I studied the Norcold manual and wiring diagram. At the top of the back of the fridge on the first heat fin, there is a thermostat switch that is supposed to turn on at 130⁰F. This switch turns on all 3 cooling fans in the back of the fridge. I checked mine with a laser thermometer. It was 135⁰F and the fridge fans were NOT running. In fact I don't think I have ever seen them run. I jumpered the bottom fan to 12vdc (you can see it by removing the bottom cover). It worked fine.
I measured 12vdc going I to the thermostat switch, but nothing coming out so I jumpered around the switch and ALL the fans kicked on!!!.
I bought a digital 12vdc thermostat control switch
https://www.amazon.com/dp/B07MNWDKZL...ing=UTF8&psc=1
I will be installing in place of the failed thermostat switch. I'll let you know how it goes.