Originally Posted by Cdusm
New wrinkle, I unplugged from shore power. The LCD display came up. I plugged in and started air conditioning normally. It ran for a few minutes, screen went blank and it shut down.
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Sounds lime you are either having 12VDC supply issues to the upper board located in the roof A/C or communication problems from that board (which supplies the 12VDC power to your CCC-I) to the t/stat.
Remove the inner shroud on your ceiling and look for the red and black wires going up into the A/C check the connections for tightness and possibly even re-make those connections with a proper crimp connector and tool. Also check the fuse that supplies the power to the A/C unit. I would change it regardless, as you need to be certain that the upper control board is getting full and proper DC power. I would also check the voltage there to be sure that it is receiving 12.5+ VDC. If you are plugged in, you might see up to 13.6VDC from the converter. This is fine....but nothing lower than 12.0VDC. If you see this, you have other issues with your DC voltage supply (battery) system.
You will also see an RJ-11 union where 2 phone-type plugs enter it. One wire will probably be gray and the other black. I would also replace that union, as they are a known source of problems.
After all of this, try your unit again to see if it comes on and stays on. If it is still having 'issues', it might be the upper relay control board and might need replacing.
\Of course, there is also the possibility that the CCC-i itself is intermittent and needs to be replaced. This is very difficult to test without another t/stat. If I was there doing the diagnostics, that is the first step I would take as it is also the easiest. All of the other steps would come later............