I the "Use/Store" switch set to "Use"?
When you turn on the Fridge: you can set it to automatically find the power sources available, and let it do it's thing...
One more thing: you'll need to get the propane actually running through the lines. (They're probably full of air right now...)
Get your propane stovetop running for a couple of minutes, and then try to switch over to propane power with the Fridge...
Good luck!