Dometic CCC2 with older 620525?
The conversion circuit board is for the new ac unit to old 5 button thermostat. I dont think they make one for your old ac to the new thermostat at any price. Return it and buy / use a 5 button , they are still available. That the cheapest way to go
Or there is a new company that makes a digital thermostat ( you can control it with your phone) $$ 250 bucks that might work .. they make them in many types with one for those older ac units I canít remember the name but itís the same company that makes a soft start unit for them.
2003 Beaver Marquis
2002 Ford Escape toad
2016 CargoMate Trailer