norcold not working properly

1. Cleaning the flue and burner is ONLY for LP operation. 120 operation the flue is not a factor. Have you tried on electric?
2. Frost Chrystal's on the freezer back wall will not stop the lower section from cooling correctly. You really need to get a digital temp of the actual freezer temp and the lower temp.
Freezer below 10 degrees
refer below 40 degrees Doug

Here is a service manual that includes your model.......LINK

Pg. 30 discusses flue with diagram

2x on defrosting. If we turn our off and open the door it happens in fast order.

As noted the frost prevents the heat inside of the box to get to the cooling unit that removes the heat.

Start by defrosting the frig/freezer. Frost does build up and can affect the efficiency of the cooling. We live full-time in our rv and I have to do this 2-3 times per year. If helps to initially cool if you turn it on for a few hours and then stock cold drinks, frozen foods etc. Never unrefrigerated items like warm pop,beer etc. If you are doing this your frig will take a couple of days to get cold.

How long did you let it cool down? Mine usually does in just a couple of hours, but occasionally it freaks me out when the freezer gets cold, but after many hours later, the fridge is still warm. The manual says 24 hours. I woke up the next morning and it was just fine.

Need to access the back of the fridge from outside the unit. Turn off the fridge. Behind that panel you'll see a tube that goes to a steel chimmney/flue. There should be some screws there. remove those and open up the flue. You need a nice nylon brush to run up the flue and clean it out. Once done clean the burner tip and restart the fridge.