Water Under the Crisper Drawer, and the Tube Behind It

Cleaning refrigerator defrost drain tube: two kinds of water, not one

A refrigerator handles a surprising amount of water it never advertises, through two systems that share nothing.

Melt water. Every defrost cycle warms the evaporator and melts the frost off it. That water runs down a trough at the bottom of the coil, along a tube, and into a shallow pan under the machine where heat from the compressor evaporates it. The whole path is inside the cabinet and none of it is plumbed.

Supply water. A plumbed cabinet carries mains water through a shut-off valve, a filter, an inlet solenoid, sometimes a tank, and then out to the dispenser and the ice maker.

Nothing about those two is shared, which is why "it is leaking" is not yet a diagnosis. Where the water is decides which one you have.

Where it is, and what that means

Under the crisper drawers, or pooling at the front of the fresh food compartment. Melt water. The trough under the evaporator has iced, the next defrost had nowhere to send its water, and it came forward into the cabinet instead of down the tube.

A sheet of ice on the floor of the freezer that reforms after you clear it. The same thing, one compartment down, and the least ambiguous version of it there is.

At the back of the machine, or running out under the toe kick. The supply side, or the drain pan. A weeping compression fitting, a saddle valve that has been dripping for a year, or a pan that has cracked.

Only in the hours after the ice maker ran. The fill valve or the fill tube — water going somewhere other than the tray.

Immediately after a filter change. The housing. This is the single most common cause we see that gets blamed on everything else first, because a cartridge a few millimeters proud weeps only when the dispenser is used and nobody connects the two events.

Finding out for certain, in an hour

Dry everything. Put a folded piece of kitchen paper in three places — under the crispers, under the toe kick at the front, and on the floor behind the machine — and come back in an hour. Whichever one is wet is the answer, and it costs nothing.

Why the drain blocks here

The trough under the evaporator is the coldest wet place in the machine. It collects the small debris that gets everywhere in a refrigerator, and in a humid house it collects far more water than the design assumed, because every door opening admits air that is close to saturated.

Once a plug of ice forms in the tube below the trough, the machine is in a loop: each defrost adds water it cannot drain, that water freezes at the blockage, the blockage grows.

Clearing it properly

The visible drain hole at the bottom of the back wall is not usually where the blockage is. Hot water poured down it melts the top inch and refreezes an inch further along, which is why this problem so often "clears" for a fortnight.

Doing it properly means reaching the trough, which on most cabinets means taking the rear panel of the compartment off, thawing the coil, clearing the trough and the tube, and checking the tube actually discharges into the pan. It also means finding out why it iced — because a drain that blocks once will block again unless the reason has gone.

One thing not to do: nothing metal near the coil. The evaporator is thin-walled aluminum and a screwdriver through it turns a drain repair into a sealed-system repair.

The related problem worth checking at the same time

Frost and a leak usually arrive together, because they have one cause. If the trough has iced, the coil above it usually has too — and a coil sealed in ice is a defrost problem that will start affecting the temperature in the cabinet within weeks.

LG publishes dS for the sensor half of that circuit. The heater has no code at all and is measured. If you have water under the crisper and frost across the back wall of the freezer, that is one visit rather than two, and it is worth saying both things when you call.