This is caused by a clogged defrost drain, you will need to remove the back cover of the freezer to access this,
Here's a little trick I've used for over 10 years now, and it's saved countless return trips on refrigerator jobs.
One of the most common problems I see with frost-free refrigerators is drain freeze up. This is usually caused by the defrost drain clogging, then freezing. On older units, it can also happen when the insulation around the drain gets 'waterlogged', as it usually does over the years, and no longer keeps the drain above freezing temperatures.
The first symptom, at least in top-mounts, is water under the crisper drawers, on the floor of the refrigerator section.
Before I found this little trick, this was a frustrating problem that was hard to keep from recurring.
Now I keep a handful of 'drain heat exchangers' in the truck, and use a dozen or two most summers, when humidity is highest and refrig. drains have to handle the most water.
These are easy to make. Just cut a piece of #12 copper wire (strip from regular 12-2WG 'Romex' household wiring ) about 6 inches long and bend it around a 1/4 inch round rod. A screwdriver shaft works well for this, but any 1/4 inch dia. piece of metal will do. They look like this.
Now when your refrig drain clogs and you find the trough under the evaporator full of ice, here's what you do. Clear the ice, open the drain
and hang this little piece of copper on the defrost heater, so it extends down the drain. On most units, this is a black rod under the evaporator coil.
This heater is responsible for melting all that frost that we don't have to deal with since the advent of Frost-free units, and it glows a dull red during the defrost cycle, so there's plenty of excess heat for our purpose.
Anyway, since copper's such a good conductor of heat, some of the defrost heater's energy will transfer down the copper wire, into the drain, and keep it open. What I like to call 'stupidly simple', this uses no extra electricity and works very well!
One precaution: hang this piece of copper *loosely* over the defrost heater. Don't squeeze or crimp it on, or you risk damaging the heater.
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