If it runs and then stops: Control Board
Just to add, ours (1988, Dometic R2605 series..) would run for 6 to 18 hours (gas or electricity) and then cut out and stop.. Did trouble shooting (no broken lines, no ammonia smell, no leaking fluid, and good wiring to back of fridge..) and answer was defective Dometic Control Boards..
Bought Dinosaur Board (components not buried in epoxy and don't overheat..) and replaced, and have no refrigerator issues since (1 1/2 years..). You can do Google search on Dometic and Dinosaur and control boards to find dealers (mail order works OK) and ID model number for your unit, if that is problem..
In Theory, there's no difference between Theory and Practice, but in Practice, there is usually a difference...