They don't install the 3way fridge any more. The inside fridge runs on either AC or propane.
It's my understanding the outside fridge is just electric.
In order to run the big fridge off propane, you also need 12v power for the electronic controller in the fridge. Set the switch to Auto and it will use the shore power (120v) when it is available, and switch to propane when you disconnect from the shore line.