1. 5 Button tstats rarely fail.
2. You did not state IF you had a display on the wall tstat. DO YOU?
3. The 5 button CCC uses a Phone cable type communication and is extremely difficult to test without using a test cable.
4. The Roof AC units run off 120 power and the tstat runs off 12 volt power from the FRONT Zone 1 AC unit.
5. Odds are you have a corrosion issue at the front Phone type cable at the front AC connections. This is probably true if you have Lo Profile Penguin units on top.
6. I would NEVER use a OEM support for my diagnosis and troubleshooting. They are NOT trained Technicians on the phone.
7. IF you have no tstat display then the odds are the problem is at the front upper AC unit communication connections. Doug
