We have a 982 Norcold Refrigerator on our houseboat on Lake Powell. I think it was installed in 1977 (it's a little old). It works fine when the outside temp doesn't go beyond the 80s, but totally shuts down when it is hotter. Do I need to replace it with the same size but more efficient up to date refrigerator, or is some maintenance required and what could we do? Thanks for help. Hermine