Our Dometic (not the same model) will auto switch to propane if there's a problem with the electrical heating element or 120 voltage. We have experienced this when the campground power went out and the system functioned as designed, we had no loss of cooling. However, I do know all Dometic fridges need to have a constant 12 volt (battery power) for the system to work properly. It does sound like you lost battery voltage.
The refrigerator model NDR 1292 require a continuous 12 volt DC supply.
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Pilot---Mark :C, Co Pilot (boss)Nancy:R
Children:
Alyssa :?, Corey :p, Matthew:h, Kaylyn :B
Dogs: Shih-Tzu's(other children)
Max , Shelby, Twiggles
TT 2001 Sunnybrook 2708 SLE
TV 2004 Ford Super Duty F-250 Diesel 6.0
Yamaha EF3000iSE/Honda EU2000i