Silly me. Here I was being caught sleeping through class. Again.
It seems that for a number of years there have been problems with "Four Button" thermostats for Duo-Therm (Domestic) AC/heater systems. In retrospect, I have found that over the last 6--8 years, there have been numerous posts concerning this problem, but apparently I was totally oblivious to them, because I wasn't aware that there was a potential problem. Shame on me.
Apparently, over the last number of years, Dometic has changed the thermostats at least three times. The kicker is that that they apparently don't maintain any back parts, so that our only alternative is to not only change the thermostats, but to also change out the boards on the A/C units. At the cost of several hundreds of dollars.
I have found two places that, in an effort to respond to the market, are taking the old thermostats, reconditioning them, then taking your old thermostat and rebuilding it.
1. William Hendrix
william hendrix - Home
2. Frerichs Electronics LLC
I have no connection with either one of these companies. I only found them through avid research.
To be prudent, I suggest that you store this information in case you need it.
If you have a Five Button Thermostat
beware. I believe that they are rapidly headed toward the same end.
Good luck, and good RVing.