If you unplug the fridge it will cool to proper temp. After a while it will only cool the fridge to about 47 deg. Could this be the defrost thermostat. The circuit boards have been replaced.
It sounds like you may have a defrost problem with the unit. Check and see if there is any frost build up on the back wall of the freezer. If so, you will need to test the defrost heater and the defrost thermostat. They should read closed for continuity when cold. You can test this with a multi-meter TJMA-DMT3. I will include a link at the end to assist you how to use the multi-meter if needed. If both parts are good, you will need to replace the defrost timer. Once the problem is repaired, you will need to thaw out the ice on the coils before the unit will operate properly. http://forum.appliancepartspros.com/oven-repair-including-ranges-cooktops/4810-how-check-continuity-ohmmeter.html