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Parts for Frigidaire FRT18KC3BW4 Refrigerator - AppliancePartsPros.com

Does the unit have an ice maker?
If yes then it could be that the water valve for the ice maker is not closing [properly.

If there is no icemaker then the water is probably from the auto defrost re: the drain tube is blocked. Looks like the water drips down into the control module at the top of the fresh food section then out the back and down the drip tube.

I would check that it is clear.
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.