HI.
If the evaporator fan running check for 1250VAC at the compressor.
If the proper voltage is present check the compressor's pins for continuity between them and the ground.
Compressor checks out fine - replace the relay/overload.
Here are the breakdown diagrams and
Replacement parts for Roper RT18DKXBW20 REFRIGERATOR | AppliancePartsPros.com
Thank you. Post the results.
Simon.