Are there two letters at the end of the number?
Your unit is under recall. If you have not had it done You will have to call Whirlpool to get it taken care of. The most likely issue for the defrost problem will be its control. It will be #13 in the look up under "controls". You may ask the service that comes to your house to do the recall to bring one and see if they will istall it at a lesser rate because thay are already there.
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If not you can use part# XXXXX at your local store.
You will have to get rid of the ice or it will warm up more. Unplug the unit and remove the rear panel of the freezer. Two screws at the top of the lower panel inside the freezer. Use a hair dryer with a GFCI protecter to defrost the ice. Have a few old towels on hand there will be more water than the pan can take. Put it back together and you will be good for a week or more. You can also go to the super market and get about 2 pounds of dry ice and wrap it a couple times with newspapper. Place it on the top shelf this will get you through the night. Also place as much food in the freezer as low as you can. Remove and dump -the ice bucket and turn off the ice maker untill the unit is repaired.
Thank you let me know how it turns out...