I'm thinking it's probably one of two things. First, plug in the coach into the correct 30A outlet and take a plug-in appliance (fan, light, etc.) and plug it in inside. If it comes on, that should determine that the converter is OK.
Now for the refer...does anything on it work? If it works on gas and not electric, that's a good sign. If nothing at all works, that's ugly. My only suggestion here would be to take the circuit board out and visit a local dealer with it. They should have a plug-in tester to see if it is good. It might be a good idea to call first to see if they have it...and talk to a manager to make sure they do have one. If the board is bad, there's nothing much that you can do to fix it other than buy a new one. I don't know the cost of refer boards off the top of my head, but I recall my WH board (which I would think is similar) was about $160.
Also, if it is the refer, make sure to go in prepared with the make and model of the refer, which is found on a sticker inside the cabinet itself. The same goes for the converter if you have to order a new one. It's unlikely you'll be able to get an exact replacement, but you'll need to know the capacities of the current one for a replacement. For the refer parts, the dealer should have access to a program to look up RV appliance parts, and it must be looked up by make and then model (and then even more numbers are required if you need a part for A&E awnings, which are on the tube or hardware). So, my best advise is go in as prepared as possible.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9473.8 (as of 6/18/21)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR