What can cause my rv dometic fridge model # rm 7732 not to get cold

Dirty coils under the unit is the most common problem, but I need to know more in order to help you. Many times you will need a volt/ohm meter to find out what is wrong with it. You cannot just guess at it and go changing parts because that almost never works: There are too many parts and you have to fix it perfectly or it will not work or it will fail again quickly. When cleaning the coils remove rear cover (unplug unit first) and spray coils down with some kind of liquid soap, including the fan blades. Then wash off with water from hose nozzle and vacuum up with wet-vac. Make sure fan runs after you plug back in (Keep water out of motor.) and replace rear cover as many units will not work with cover removed because cover is needed to route air through coils. Give us brand and type along with model number (on inside of door) and I can send you a manual.