Here is what the manual says about the thermistor. Probably a good idea to test it first, then you could try a rheostat and experiment with lowering or raising the resistance and see.

5.1 Thermistor
Disconnect the thermistor harness from the P2, 2-pin terminal on the lower circuit board. Place the thermistor in
a glass of ice water (more ice than water), approximately
33° F to 35° F. Wait 8 to 10 minutes. You should get a
reading of approximately 8,000 to 10,000 ohms. Always
test from the wire side as shown below as not to create a
connection problem at the P2 connector.
NOTE: The RM1350 will not run constantly when the
thermistor is unplugged or becomes an open circuit, because the RM1350 has a water tank in the refrigerator
to provide chilled water for the dispenser. Failure of the
thermistor will cause the unit to stop cooling.

I think I actually remember seeing some kit that adds a rheostat.
Ahh, yeah, here is was - https://www.dinosaurelectronics.com/Dom_adj.htm

Thanks Ray for the quick reply. Sounds like good advice. Will test thermistor, then look into rheostat.

Our Dometic runs too cold. Freezer: -19c and Fridge: 6c though sometimes down to 2c in fridge. Actually ideal I guess but occasionally food freezes or fins ice up. This is with the thermistor slid down to it’s “warmest” position possible.

We have seen a few videos installing fans to help circulate air, both inside and at the back of the fridge. Has anyone had success doing this?

Ours is like that too. I just make sure to put things on the top rack that don't easily freeze. I remember our old Dometic never got near as cold, then when we had it fail (ammonia leak from cooling system piping) We got a new one under an extended warranty. Though it was exactly the same model number I noticed the cooling piping in the back was way different and the thing cools drastically better even when the slider is down low.
I bet they saw the competition coming from residential-style fridges in the RV market and redesigned things for better cooling and maybe a faster startup. As far as ice on the fins, I think its to do with the warm humid air from when the door is opened condensing on the fins, I get it in the summer in BC but during the winter in the dry desert air, it doesn't happen. Every month or so I melt it off with a blow dryer.

Our old fridge had an OEM fan and it was noisy so I swapped it out for a quieter computer fan https://www.loveyourrv.com/replacing-my-noisy-dometic-dm2652-rv-fridge-fan/

When I got a newer model fridge it didn't have any fan, but ended up doing a review for a fan company and added them to test. They are still there and make a difference when it gets really hot out.
https://www.loveyourrv.com/installing-titan-rv-fridge-and-roof-vent-cooling-fans/

To increase cooling in my Norcold I use one of those battery operated fans pointed directly at the fins in back. This made a noticeable improvement in the temp.- maybe 2 or 3 degrees cooler. It has the same effect on my daughter's Dometic fridge too.

ok tnx Ray. Thought it strange because other folks are always saying how they could not get them cold enough and we have our thermistor as far down as it can realistically go on the fin. But rather too cold than the other way. Our next Dometic serious problem is a stinky leaky model 300. Our second under warranty. The dealer is going to try and fit a 320 (porcelain) in on Wednesday we hope as we leave for a month starting Friday. We had a 320 in our previous TT.

Good news, tested thermistor in ice water and it had 9600 ohms. Since it was working I ordered the part you suggested. Put in the rheostat and lowered it a little each night. Took a few days but now it is down to 0 degrees in freezer and 35 degrees in refrigerator. Thanks again for the advice.

Nice, thanks for the update