As a general rule, I would first check to see if the compressor is running. After that check that the evaporator fan is turning. Look for frost on the back freezer wall, which would indicate a defrost issue. Check that condenser motor is operating. If this checks out, look at the condenser coils for blockage. If all this checks out ok I would then check for appropriate heat in high side coils. On this particular unit if everything checks good, I would suspect one of the cold controls. One has a capillary tube that feeds into the freezer side that actually cycles the compressor at desired temperature. The other opens and closes the air damper to control fresh food side temperate. Good luck.keep it simple and don't look past your problem.