What year is your Seneca? On our '15, the Norcold fridge has three settings - LP, AC, or auto. AC will only function if the shore line is connected to a power source or if the genny is running. AC will be "preferred" in auto mode, and you definitely don't need to turn off the gas to get it to switch to AC.
Just confirming - when you say you're plugged into 110v, you mean you have your shore line connected to a 110v outlet through a dogbone or adapter, correct?
If that's the case, check and make sure you don't have a breaker tripped (ours has a specific breaker for the fridge). You might also check and see if the fridge plug (located in the space covered by the outside access panel) has somehow worked itself out of the outlet it is supposed to be plugged into.
Ty & Deb Montag
2015 Jayco Seneca 36FK
2014 Honda CR-V toad