The fridge gets its cold air from the freezer through a vent(damper)between the freezer and fridge.The fan in the freezer blows air through it.Make sure this fan is running. You may have to hold the door switch in for itto run.
There is a flap you adjust withthe fridge temp. control. Make sure it's opening and closing when you adjustthe fridge temp.The problem could be the electronic control ifyou have one or the mechanical linkages.
ORThe evaporator coil behind the cover on the backwall inside the freezer will ice up under normal conditions. Every 8 to 10hours for around 20 minutes the defrost timer (or in most newer models the electronicadaptive defrost control) will turn the defrost heater on tomelt the built up ice. There is a defrost thermostat which prevents the heater fromoverheating the freezer by breaking the heater circuit when the temp reachesclose to 32 degrees F. The entire cooling system shuts off during the defrostcycle and starts back when the timer advances through the cycle. If this ice is not melted it will continue tobuild up until the air can’t flow over the coil to circulate the cold airthrough the freezer and into the fridge. The temperature change in the fridgeis usually noticed first followed by the freezer. If the defrost thermostat is bad it can prevent the heater fromcoming on OR it won’t turn the heater off when it gets too warm. It is clampedto the evaporator coil at the top to sense the temp. If it appears to bemisshapen it is bad.With an ohm meter it should show continuity whencold and none when warm.You can also bypass the thermostat to see if theheater comes on then. If it does then you know the thermostat is bad and needsreplaced. The defrost heater islocated on the evaporator. It is in a tube which is at the bottom and can alsogo up the sides of the evaporator. On some types you can see a burnt spot ifit’s bad. With an ohm meter it should show continuity from end to end whendisconnected from the wiring in the freezer. You can also test the wiring forvoltage when it’s in the defrost mode. Ifyou have a defrosttimer youcan test it. It can be located under the fridge behind the kick panel on thefront. Some are in the fridge with the controls at the top. You can turn the defrost timer till it clicks and everything shutsdown. The heater should now come on. If it does, replace the timer because thatmeans the timer is not running. If itdoesn't, check the heater and defrost thermostat. Turn the timer again tilleverything starts back up to end the defrost cycle. If you have an adaptive defrost control instead of a timer,replace it if the heater and thermostat test good. It is located in the fridgewith the controls in some models and on the back in others. If you need help finding your model number seehere> http://www.appliancepartspros.com/modelnumber_locator.aspx
To locate your timer, motherboard, control or adaptivedefrost control , enter your model number and search for the part or post backon Fixya. http://www.searspartsdirect.com/partsdirect/index.action?psid=26129238&sid=PSx20071217x00001a