Dometic RM 4224 won't cool on gas or electric. The stack in the back gets super hot, the fridge is not cool at all.

SOURCE: Dometic RM2652 Refrigerator Problem

Check the flu at the back is clean

SOURCE: AC,DC, gas RV fridge Dometic

You more than likely need to replace the control cable between the upper and lower board. It comes as a kit with the upper board. You can also do a bypass test by unplugging your thermoster from the circuit board. The thermoster is the temperature control for the refrigerator nothing to do with the freezer.
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SOURCE: Freezer working, fridge isn't.

It is possible that your cooling unit is failing due to a blockage. The solution used to cool starts at the top of the fridge and works its way to the bottom. If there is a blockage in the cooling unit it could produce the symptom you have explained.

SOURCE: Camper fridge dont cool

I also had the same Model Make. I removed my fridge and placed it upside down, occasionally shaking fridge within a 24 hr period. This seemed to re-mix the ammonia solution and the fridge is working.
This may work for you but look for yellow stains if you see any your fridge is leaking and would require repair.

SOURCE: I have a Dometic RV fridge that wont get cold. it

It sounds like your cooling unit is going out. Here's a couple of things to check. Do you smell any ammonia when you open either one of the doors? When you look at the rear of the fridge, do you see anything that looks like rusty water that has run down any of the metal tubes and dried up? If the answer to either one of these is "yes", then youll need to start looking for a new fridge or replace the cooling unit on the one that you have.