Refrigerator won't cycle up

There are 3 parts that actually control cooling cycle: Temperature Thermostat, Defrost Timer and sensor/relay on the back side of the appliance. If fridge cycles up after you turn small knob on defrost time (you'll hear click, problem lies between first two components.
Replacing them is really easy. Make sure you handle thermostat wire carefully. Check for connectors holding firm.
Use schematic diagrams you may find at this site.

Good luck.