
I'm not sure of your intentions about your 5er. Do you plan to leave it parked where it was? Or, do you plan to use it as it was designed, mobile to see our great Nation?
First, the refrigerator. From your description it sounds like the fridge has a faulty PC board, and it has switched to constant cooling until it can be serviced. If you cannot move your 5er now, look in the phone book or search the internet for a mobile RV service technician near your location. They should be able to diagnose the refrigerator and repair it on-site.
Without knowing how the black tank was bypassed I cannot address that issue. Again the mobile RV technician will know what to do. If you prefer,and are a handyman,(person), you can have the problems diagnosed, then purchase the parts and perform the repair work yourself.
The refrigerator
must have a good 12V house battery to power the PC board or it will not work. The same is true for the furnace.
I hope my opinions help some, if not, others more knowledgeable than I will join your topic questions.