Anthony are you sure the fridge is a three way power fridge? Most trailers have two way fridges, propane gas and 110VAC electric. If the fridge is working on gas and electric you do have 12VDC power to the fridge which runs the circuit board.
If it is a three way fridge then you need to check the fridge circuit board for a blown fuse to the 12VDC heating element. I'll PM you a contact # and we can talk more.