I have a Norcold N621 refrigerator in a recently purchased 1999 Arctic Fox 22H. Refrig has worked fine in AC mode when camping at full hook up sites but does not cool in gas/propane mode. There are no error codes and flame starts right up in gas mode, flame looks normal. What might be problem? Bad thermistor on cooling fins? Blocked or missing baffle in gas flue? Bad temps sensor or electrical connection affecting propane flame modulation? The fact that electric cooling works indicates there is at least some refrigerant in the cooling system. No refrigerant leakage is visible or obvious. Comments/suggestions?