Colleen,
Probably a loose wire, look at my post on the Dometic thermostat problem.
When I first got the Monte, I checked the 12 volt panel, one of the main wires feeding the panel was just inserted into the set screw, I got 3 full turns on it. That would have led to major problems down the road.
Some trouble shooters, RV dealership's maint. people, just start replacing items in hopes of finding the problem. We call them 'Parts changers' in the trades.
Some are very good, but our chances of getting them may vary between slim and none.
Good luck with your problem, I know how frustrating this type of problem is, when you have a loved one depending on their work for comfort, and possibly survival....
Take care, Ozz
'07 3400RL 2nd RTU
2 Golf Cart batteries 3,000 watt inverter, automatic transfer switch
Honda 2000 Generator, 2nd one and twinning kit coming
Maytag's with 220 Dryer
Stationary domed Sat. dish
LCD 12 Volt Amp gauge
LCD Tank Monitor
3 added 120 volt outlets
On Board Air; 12 Volt Viair 450C compressor
2006 Ford PSD 4x4 Off Road Lariat
Hadley Air Horns
Truck inverter with 110 volts for laptop
Color Backup Camera
Awning lock