After weeks of playing hide and go seek for the fathom 4th controller, I finally determined that there was NOT one. Frank and Tom were right as usual!
With the aid of a DVM, Fluke wire tracer and a oscilloscope I was finally able to find all the problems. It was a wiring issue. It seems that Dometic changed the wiring for the furnace controls in the AC control board. They also changed the wiring of the two black RJ11 communications cables from the control board. One of the figures in their installation manual shows that the communications cables are straight one to one and in another figure they show that the cables are crossed.
What I discovered is that the RJ11 cables are crossed in both positions in the controller wiring. I also discovered that Monaco used a coupler for the silver satin communications cables that crossed them again. With all the communications cables crossing the 12 VDC that powered AC zone 2 and 3 was never getting to the AC control boards and the communications from the thermostat to zones 2 and 3 were never getting to the respective controller boards in the AC units.. After making all the cables pin 1 to pin 1 etc and getting straight through couplers the units all work. Connecting the proper wires from the AC control board to the correct furnace zone wires now all three systems and furnace zones work properly.
The Nightmare of how this ever worked at all will always be a mystery. But everything is now working in the HVAC/AquaHot systems as far as the inside heating and AC is concerned.
Thanks again for Frank's and Tom's assistance. I have certainly learned a lot about how Domectic, AquaHot and Monaco wiring all work together.
