I have my fridge hard wired to a fuse block in the back of my runner. I also have the AC cord plugged into the fridge. When I'm home for a couple days I unplug the dc cord from the back of the fridge then run an extension cord to the truck and plug in the AC. My question is do I need to unplug the DC before plugging in the AC power? Does the fridge switch over to the AC even if DC is still being provided or will doing this fry something?