The air/HP on the roof is a generic unit capable of fitting several applications. The wiring to it, the switch settings on the circuit board, and the type thermostat used determines how a given application works. Then there is the flat ribbon cable that ties all the units together. If they cannot digitally talk to each other, they will not work the way they are designed to work.
You need to make a decision as to what you want to do. If you want to stay OEM from the factory, good luck. If you want the system to work properly, you need to make some changes. Many of the components are no longer available. The new air/HP units come with new designed circuit boards that Are NOT compatible with what you have now. Any failure with what you have now requires a very costly complete change out of all associated components. Then there is the flat ribbon cables that ties the units together so they can communicate with each other.
We full timed in our coach for 6 years. In order to keep the DW happy, I had to keep all the systems working the way she was use to being working. There are not many coach owners left that has the HP/furnace found on our coaches. Most had the Aqua Hot system.
I suggest that you get out the manuals for your air/HP units and familiarize yourself with each of the components, how they are wired, the many option settings, to better understand what you are dealing with. Chuck B