The power switch on bottom of the older dometic thermostats had no physical support. The solder joint can easily crack with normal use of the power switch. In the early stages, your AC will turn on and off while you are going down the road and might not turn on at all depending on what you had for lunch (hee hee). It gets worse with time as the cracked solder gets junk and pollutants in the crack and then it wont work at all.
Take the board out of the case and resolder the power switch. Be sure to use electronic solder, not plumbing solder.
Check the circuit traces where the switch is mounted to make sure they are not cracked. If the trace is broken, you can scrape the green insulation off the trace carefully with a small razor knife. Use a short piece of wire cut off a resistor to bridge the break and make it stronger too. Cut the piece of wire too long and bend the end up so you can hold the wire in place with small needlenose pliers while soldering, then cut the end off with a little wire wire cutter.
On mine I resoldered all the joints because there were a lot of cold solder joints (which crack easily). You can tell a cold joint because it is not shiny. Do this carefully with a fine tipped iron, and inspect it to make sure you did not make any solder bridges.
After soldering, clean rosin off the back of the board with a clean toothbrush dipped in rubbing alcohol. You do not want the impurities and chemicals in the rosin to attack the solder joint later.
