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Unfortunately this is not an easy issue to fix on these bottom freezer top refrigerators. You will want to unplug the unit for 24 hours to allow all the ice to thaw out. Once the ice is thawed out, the best way to clean the drain line is from the bottom up because going at it from the inside is really difficult. If you pull the refrigerator forward and remove the bottom access panel and locate the rubber hose which comes down directly from the middle or so of the freezer floor toward the back and use something like a turkey baster to shoot hot water up the hose. Once it's clear and you can blow air through the hose, you're good to go again. Also, if you have the ability to just unplug the refrigerator for 24 hours that'll thaw all the ice out and them you can just blow air up and clear the drain out.
The other option is to remove the drawer out of the freezer, then remove all the racks and rails on the side walls. Remove the plastic vent directly in the middle of the back panel toward the top. Remove all the screws going into the back panel because the ultimate goal is to remove the back panel. Once the back panel is removed, you can use a hair dryer to thaw the drain line out. Pour hot water down the drain hole until it's draining properly again. Once it's draining properly blow compressed air down to make sure it's clear. If you don't have compressed air, use a turkey baster to make sure the drain line is clear and draining properly. Cut a solid copper piece of wire about 6 inches long. Wrap it around the defrost heater a couple times just above the drain hole and extend it 2 inches into the defrost drain hole. That will transfer heat into the drain hole when the defrost heater turns on and will prevent the defrost drain line from freezing over in the future.
Also, if you didn't want to use a copper wire, there is an actual kit made which you can wrap around the heater if you wanted to buy the actual kit to perform this task.CLICK HERE
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