I had this happen, same situation as yours. I tried everything, blew out the stack with compressed air, replaced the regulator at the propane tanks. Then finally was at a loss, so I got a mobile RV guy who charged a lot of money. He checked the propane pressure at the stove, but did not check it at the propane burner in the fridge. His diagnosis was it was the propane regulator at the back of the fridge. He didn't have one, so I then ordered one and replaced it at his direction. Problem didn't change -- fridge worked fine on electric but not on propane.
Our fridge is in the slide, so what I eventually discovered is that the rubber propane supply line in the slide, which zig zags in and out held by a metal zig zag mechanism, had kinked. So I had flame, but it wasn't enough. I had a new custom hose made at a custom hose place, installed it, and problem fixed.
I can tell you that it is very very hard to tell by looking at the flame if it is getting enough propane. Our flame hardly looks different now that when it wasn't working on propane.
So add to your list of possible causes, the propane regulator that is at the back of the fridge inside the plastic accessible panel. That wasn't the cause of my problem but it is a possible cause.
Follow up to my story: Called up RV mobile tech bloke and complained that he charged me a lot of money for his service call and diagnosis and that I did exactly what he advised, but that it fixed nothing, PLUS, I was out $40 or $50 for the fridge propane regulator. To his credit, he refunded his service call charge, though of course I was still out the $ and install time for the fridge propane regulator.
Maybe I shoulda been a mobile RV tech guy -- they sure know how to charge!!
Good luck!
