The 12VDC electric mode was intended more as a travelling/back-up mode of operation. The propane mode is typically considered the normal use mode. I would recommend you get familure with that mode of operation and then ensure it works ok at some point. One good source of information for older RV Fridge opearation and maintenance is: RV Mobile, RV and Gas Refrigerators
Select the Technical Help link at the bottom left side of the page. There is lots of background and troubleshooting information.