I was having the "no cooling" error last year while traveling. Turned out the vent fan was bad.
If you have a side exhaust vent, Norcold requires a powered vent fan, at least with the N641. Not sure about your model. I've seen a few post where the poster said the RV manufacturer didn't install the power vent fan.
I replaced our fan and had it happen again on the next trip. The new fan had died. It was made in china. I replaced it a second time and it has worked well the last three trips. I also added an additional fan that I can turn on to help vent the heat.
Another thing that can cause the "no cooling" error is running the frig more out of level than it is designed for. I believe my N641 specifies 3 degrees side to side and 6 degrees front to back.
Joe and Evelyn