I had that problem on my first trip in our 2017 FR3 29DS . Took it back to dealer and they found broken wire connections at the AC. The access was under the plenum cover in the ceiling. Had problem again and there was bad wire in the thermostat.
Got it running, but output was poor and eventually it began leaking water from the grill. My AC is an Atwood model AC-1361 not a heat pump. There is a Dometic fix available for this problem. I called Dometic and they sent me two kits, one for each of my AC's with no cost to me. See this thread for info: http://www.forestriverforums.com/for...r3-169184.html
. I istalled them myself and every thing worked. The front AC still had a problem with low output and freezing up. The dealer determined the Freon was low, which requires AC replacement covered by 2 year warranty. Finally everything worked OK. Found up to date Dometic Atwood Air Command Manual and found the operation of the thermostat for heat etc. was not as I had been told. I was confused because I had originally been told my front AC was a heat pump and the operation of the thermostat is different between the two.