Carey,
I would start by looking at the documentation for the refer and seeing what the current draw is on the exclusive 12 volt setting.
If it is like most 3-ways, it requires an immense amount of current, because it has to run a resistance element to heat the medium that actually does the cooling (I know that sounds counterintuitive, but it is the case). My bet is that you are trying to keep ahead of a very high amperage draw and the entire electrical system (battery, alternator, wiring) is not up to it.
Is there a reason you could not run on the propane setting while going down the road? That would mean that you would be drawing only a very small amount of 12 volt current that is needed for the control circuits.
For what it's worth.
Rich Phillips
Member #27
Rich Phillips
Member #27
2019 K-2500 Crew Cab Z71
Cedar Creek Silverback 33RL Fifth Wheel
In The Past: '82 6.2 Jimmy Blazer, '93 6.5 GMC K-2500, '01 DMAX K-2500, '09 DMAX K-2500