I'm not sure what kind of diagnosis that is, but these are fairly simple systems. Under each A/C, there is a control box that works with the thermostat. From the thermostat, there is a cable that looks like a telephone cable but is wired differently. The cable goes to the rear A/C, which is zone 1, then from the zone 1 A/C another cable connects the control box to the control box under the bedroom A/C, zone 2. The furnace is connected to the control box under zone 1 A/C. So, you have the thermostat, two control boxes, two runs of phone cable, also a remote temperature sensor on the bedroom ceiling that tells the thermostat what the temperature is in the bedroom, and of course wiring from the furnace to the zone 1 thermostat.
We lost the front A/C function years ago, and after some digging, found corrosion on the circuit board in the box below the A/C in the bedroom. I replaced the box and have had no issues since, and never did figure out why the circuit board was corroded. Hopefully you can find a tech that can really figure out what component has failed. The photo below is of that circuit board.
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Bob & Becky
2012 3402RL
2012 Chevy 2500HD D/A CC 4WD
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