Kenmore side by sidecools then quits

Model 106.54789800 slowly quit cooling. I check the coils and they were badly covered with dust. Cleaned them, and hey, back to 0 on cooling and 32 on refrigerator side. But, it cools about 6 hours, I check it, and both freezer and frig are at 40 degrees. I turn it off about 10 min, plug it back in, a hey, back to 0 degrees and 34 or so on frig side. What is going on? The fans, one on the compressor, bottom, and the one in the upper freezer, both are running. Lights work, everything works. It just cools then quits. OR, rather will not get cooler than 40 in freezer and frig. I have ordered a start up capacitor, and relay for the compressor. Will that fix it?