It looks to me like the first failure suspect is the temperature control (#21 on the diagram
). Move the temperature knob back and forth next time the refrigerator will start to get warm and if the compressor will start then this is the culprit.
- The part number for the temperature control is AP2146546
Here are the breakdown diagrams and Replacement parts for FRIGIDAIRE FRT21NNCW1 | AppliancePartsPros.com