Are you saying that the flame is not right, or it is not cooling? If no flame, then of course no cool.
Did u answer if it will cool on AC?
First thing to check is for bugs. Dirt dobbers or other bees can nest in the propane areas and cause a no flame situation, check your propane furnace while you are at it.
Many other things can cause a no-flame, including a bad thermocoupler, or one that has been knocked out of place.
2004 is old enough that if the previous owner did not be very careful to never run the fridge while not level, that the fridge cooling unit is ruined. It might seem to cool a little bit, but will be so ruined inside that it will never run like new.