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Replacement parts for TBX22JBA models | AppliancePartsPros.com

Sounds like drain tube is plugged so that the water from the defrost cycle cannot drain into the drain pan.

Some units drain into a funnel like part at the top of the fresh food section and then out the back others connect directly to the drip tray under the evaporator coil in the freezer.
I cannot tell which yours is from the parts breakdown diagrams.

I would check that it is clear.
You may be able to disconnect it where it comes out the back of the fridge.
The problem with this is that it may be plugged upstream from here.
If plugged a turkey baster with warm water, an air compressor with low pressure or a wire can often be used to clear it.

Also check that it is not plugged with dust etc. at the drain pan end.
You might as well clean the condenser/compressor fan and the condenser coils while you are down there.

If it looks like stuff is growing in the tube I would flush it with a 10% bleach solution. This should kill the stuff and let you flush it out. You may have to do this several times, let it sit for 15 minutes or so between flushes.

Be careful that the drip tray does not overflow and empty the drip tral after you are done.

Be sure to unplug the unit while doing this.

Also a good idea to check/clean the condenser/compressor coils and fan since you are already working on the unit.