Electrical conundrum...

[Jem5649]

He everyone!

So I just fixed my fridge , but now I have come up with a conundrum:

The constants:

The fridge works
The outlets work when the van is plugged in
I have only 1 battery, no separate house power yet

The symptoms:

With the van plugged in, the fridge works on 120V with the input switch on any of the 3 options(Car battery unhooked to make it use the 120V)

With the 12V hooked up, the fridge seems to only work with the rear power turned on and off of the 12v regardless of whether or not I have it set on 120v or 12v mode.

With nothing plugged in, the fridge will not work (I would hope this is the case )

I am hoping that someone can explain to me how my van is wired better than me trying to take it apart since I have no electrical knowledge in terms of non-theoretical application.

Also more importantly, will the fridge kill my battery if I am plugged into 120v if the rear power is on?

Thanks much!!!