I've had this problem once before with this 12 year old fridge, so I thought fixing it would be cake.
I took out the panels in the freezer, thawed the ice, and removed the wire that I previously coiled around the heater element and put 2-3 inches down the drain tube. But after a long time, I was unable to get the drain tube to drain. Used a hair dryer, hot water, a turkey baster, and numerous foul words, all to no avail. It's hard to imagine that any ice remained in the tube. No water drained into the drip pan.
It doesn't look like the drain tube is replaceable. My guess is that it is clogged with years of tiny bits of debris from the freezer.
Any suggestions about what my next step should be?
If I need to get a new refrigerator, any suggestions about a good one that has 20-21 cu ft?