Refridgerator not cooling
 

Fridge and freezer not cooling. Replaced the defrost thermostat, but didn't work. When fridge running, a switch sound kicks in and has a slight buzz for a short time and then kicks out as though not engaging. The sound is coming from the lower back left side behind the freezer. Thought it might be the defrost timer.

Sounds like there is a problem with the compressor start relay or the compressor itself. If you need the correct part numbers then post the complete model number of the refrigerator.

Gene.