If your refrigerator is warm, but your freezer is cold, check to see if your refrigerator’s defrost thermostat is working. Check your refrigerator’s evaporator coils. If you notice a buildup of frost or ice on the coils, that might be a sign that the defrost thermostat is no longer working and needs to be replaced.
The defrost thermostat is a bimetal thermostat that opens to shut off the heater and end the defrost cycle.
This part can be tested for continuity using a multimeter.
Find a new defrost thermostat for your refrigerator http://www.everyappliancepart.com/Category/Refrigerator-Parts/Defrost-Thermostats