So since both furnace and fridge are side by side it would not surprise me that the 12vdc feeds to them are possibly a common fused feed from your DC fuse panel. I think you said all fuses looked good. I would be tempted to pull the fuses and re-seat them again in case you have a poor connection(s). I would also be tempted to open the failed appliance outside that is closest to the DC/converter fuse panel and see if you can identify the 12vdc feeder wire and trace it back as far as possible just to see where it goes and that it is in good condition. You may find an in line fuse long that path or may also find a multiple/splice (if it exists) that goes to the other failed appliance as well. Sorry I can’t suggest something else, but it just seems that those two closely located appliances failed at the same time......sounds as you said like an open fuse somewhere. The other thing is could they have a common ground wire that is not making good contact to chassis somewhere?
Others may have better suggestions for you.
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