Hi.
What you have there is a bad defrost system.
Locate the defrost timer in the control box in the fresh food and using flat screwdriver slowly turn the shaft CW until the fridge stops. Check in 5 min. if the defrost heater came on.
If it does - replace the timer
Part number: WR9X520 
If not - open the rear panel in the freezer and check continuity of the defrost thermostat
Part number: WR50X10010 
And defrost heater
Part number: WR51X464 
The defrost thermostat must be ice cold when tested.
No continuity - replace that part.
Here are the breakdown diagrams and
http://www.appliancepartspros.com/pa...odel_id=224827
Post the results.
Simon.