Dometic fridge fins icing

From manual
automatic cooling unit cycling system and low ambient control The refrigerator has been design with an automatic cooling unit cycling system that helps reduce frost build up in the fresh food compartment. The first automatic frost reduction cooling unit cycle begins 60 hours after turning “on” the refrigerator (for best operational results the refrigerator should be turned on anytime between 4 and 10 PM), and will last for approximately 120 minutes. Thereafter, the cycle will automatically repeat every 48 hours as long as the refrigerator continues to run. The automatic Low Ambient Control (LAC) ensures troublefree operation in low ambient temperatures (e.g below 50° F
Look through trouble shooting portion. There is a diagnostic test.
Manual

Think about it. Other than the little bit of moisture your produce gives off as it dries out, what would be the source of moisture inside the refrigerator? The answer is there isn't any. The moisture causing your coils to ice up is coming from outside your refrigerator. You need to prevent it from getting inside to solve your problem.

Thanks for the replies. Will do some checking next time out later this week.
What about this "Automatic frost reduction cooling unit cycle" in the manual?
Would this account for the temp rise? Different issue for the rapid frost buildup?
I use the 4 setting and normal temps are 34/35 degrees. Rises to 43/44 periodically, and then back to normal. Manual says every 48 hours, I never checked. Never had any frost until this time.

rrupert wrote:
It's my understanding that the fridge is supposed to shut off cooling periodically to allow the frost to melt from the fins. I assume that function is controlled by the control board.

Only Norcold refers have this operation. Doug

The moisture to make the ice and frost must be coming from outside the refrigerator meaning there's somewhere it's coming in it shouldn't. The dollar bill test is a great way to find out if the door gasket is at fault. The bill should have a good drag on it as it's pulled on with the door closed. There's not many other places moist outside air could be getting in other than the gasket. The drain tube on the backside should have a restriction that allows water out but prevents air from entering.

Good chance it is the thermistor!
It can be tested.
Remove it from the refer
Connect an ohm meter to the two thermistor leads. Stick it in a glass of ice water. Use a scale of around 200K. You should see resistance and as it gets colder it will change. At some point it may go completely open, no resistance. This means it has shut down the cooling unit.
Thermistor values

My Norcold automatically goes through a defrost cycle every 48hrs. Very little icing of fins.

Look for bad spot in door gasket. If air leaks in, humidity condenses out on fins and freezes. Try the dollar bill test. Close a dollar bill in door and verify that there is drag when you try to pull it out. Make sure there isn't something in the door or on a lower shelf that is holding the bottom of the door open slightly even when the latch is latched.

Some icing on fins is normal. Mine usually takes 4 - 6 weeks to ice up the fins to the point that they need to be thawed out. Only saw them ice up in 1 day when grandkids left the door slightly ajar.

It's my understanding that the fridge is supposed to shut off cooling periodically to allow the frost to melt from the fins. I assume that function is controlled by the control board.