Replacing the RJ11 com cable ends was a good attempt by Independence RV at curing the problem.
Since that failed to repair you are looking at replacing your com cable from #1 a/c (front) to CC2 thermostat. Last year I replace all three Dometic Heat Pumps and had to run a new com line between #2 and # 3 Penguin II's due to a one open wire.
Try running a temporary RJ11 cable from CC2, out the window/door to #1 A/C. If this works you know absolutely it is that run. Other thing you need to know is that the pin out of the com cable is not just telephone cable it is special to com cable. See page 9 of attached PDF for your CC2 thermostat.
You can buy the loose RJ 11 ends and the crimping tool at Home Depot. Run the com cable all the way to your roof top control board. Do not use the short com cable connector at A/C. It has reverse pin out that corrects the normal Newmar installed telephone run. If you do not want to make your own com cable you can run telephone RJ11 cable to the short connector to you # 1 A/c control board. It is harder to put in words just than show you but it is all I have to communicate with you.
Here is the $79 Klein VDV Scout Pro 2 Tester Kit
testing tool. Bought at Home Depot. Found that found the open wire. It shows pin out too.