Your motorhome is equipped with a 3-way refrigerator. That's a fancy way of saying it can run off of 12v dc, 110v ac, or LP gas. But in which order is this prioritized when set to automatic mode? I'm glad you asked!
The priority is as follows:
110v AC power. This is what your refrigerator will use by default if available.
12v DC power. If 110v AC is not available and the engine is running, this is it's next step. If the engine is not running, and you are not connected to shore power, the automatic mode will skip this and go straight to LP gas.
LP gas. This will be it's last resort if the other 2 power sources are unavailable.
Of course, you can override which power source is being used at any time by manually selecting which you would prefer.