Why will a Dometic refrigerator. Why will a Dometic refrigerator not work on LP alone. It works

Question

Why will a Dometic refrigerator not work on LP alone. It works fine on electric. It sounds like it is clicking and trying to work, but the "check" button always lights. As soon as we get the campground and plug in to current, it works fine. Our lp regulator was just changed last fall and our propane tank is also new. Any suggestions to try? Thanks, Joan Waunakee WI