Norcold works on AC not propane

A clogged stack.
The stack is right above the flame. It is about 3/4 inch diameter pipe. There is a baffle about 4-5 inches up inside.
Use a stiff but slightly flexible peice of wire. Push it up into the stack to knock loose carbon build up.
Make sure unit is off!
Be prepared for carbon to fall down. Vacuum out debris.

Baffle needs to be removed via top vent access THEN brush/clean up stack and baffle.....rust/soot impede heat transfer
Cover burner so debris doesn't fall in slots and block burner

Spiral baffle absorbs heat from flame then transfers that heat to perk tube where the ammonia flows

After brushing/clean make sure baffle is reinserted and back in place

If OP wants to remove baffle and fully clean stack, a shot gun 12 gas brush works good.
Rattling the baffle from below will tell whether there is build up of soot in the stack.

I did remove the upper access panel to try to remove the interior baffle in the propane flu but it wouldn't come up and out, would wiggle but could not lit it up. The fins looked fine, no real dirt or nests. Cleaned the flu best as I could from the top and from the bottom with a stiff wire to remove carbon, but not really much came out the bottom. Kept the burner covered doing this. Blew off the propane burner orifice with a straw. Did a fuse continuity check on both fuses, both OK. It's very puzzling. Works great on AC, propane burner fires right up. Looks to be a good steady blue flame with just the lightest trace of orange in the middle. It's either not a hot enough flame or the heat transfer is not taking place as it should. Just got back from an extended trip to Yellowstone, other than this issue all went great. I know high altitude can affect some propane systems but now back to near sea level and still no cooling on propane. ??

Is your refer in a slide? If so, you need to pull the refer to get it out.
Were you able to rattle the baffle? You should be able to do this from the bottom.

I took the fridge propane burner unit off, sanded any rust, cleaned and blew it out with compressed air. I knew the minute I fired it back up that that was the issue, now works great. Flame considerably larger, hotter, even louder. I should have done this before but thought blowing it out with a straw was enough. No. I am still kinda new to this but learning all the time. Did all those other maintenance things on the fridge cooling so I should be good. Thanks for all the feedback.

Thanks for the update!