I find this hard to believe, but I am no expert. Are there any RV techs out there with a definitive answer?
I have a 2011 Phoenix Camper with a 3cu ft Dometic 3 way. It has an auto feature that runs the fridge in the optimum mode. So when driving down the road it goes to 12v, when stopped with the engine off it switches to propane and when plugged in to shore power or generator it goes to 120ac. There is a manual over-ride, so if the battery is low you can set it to run on propane when driving to more quickly recharge the battery. I just installed a 12v fan in the lower compartment at the back of the fridge. It seems to help handle heat build up back there and help cooling efficiency.
I have the same Dometic RM2354 that DanoT has, but the AUTO setting on mine as described in the manual only switches between AC and Propane. To switch to the DC mode (only used when I'm driving so the truck alternator provides the DC), I have to manually change to the DC mode. So when I stop to go shopping or for the night, I have to manually turn off the DC mode and put it back on AUTO. If you have this refrigerator, it works great but don't let it run your battery down quickly by leaving it in DC mode when the truck isn't running. !Learned the hard way!
