Every summer we get calls about built-in refrigerators sweating, and a good proportion of them are not faults. A cold surface in a room at eighty percent relative humidity will condense water, and a kitchen on the Intracoastal side of Jacksonville Beach with the doors open to the deck is exactly that room.
The useful skill is telling normal condensation apart from a seal that has genuinely gone, because the two look similar from three feet away and only one of them costs money.
Outside the cabinet is usually physics
Moisture on the outside of a door, on the frame between two compartments, or along the trim is the room meeting a cold surface. Built-ins have heaters in exactly those places to manage it, and when the room is humid enough they cannot keep up.
Things that make it worse and are not faults: the door being opened frequently, the room being hot, an air conditioner that is undersized for a kitchen with a professional range in it, and a house that gets its outside air from a deck at the water’s edge.
Things that suggest it is turning into a fault: sweating that persists in a room that is not especially humid, sweating that appeared suddenly rather than seasonally, or sweating accompanied by anything happening inside the box.
Inside the cabinet is a seal
The gasket on a built-in does two jobs. It seals, and it holds the door in the right place while doing it. When it hardens — and coastal heat and humidity harden them steadily — it stops doing the second job first.
The evidence is inside:
Frost building on the evaporator or the back wall of the freezer, because humid room air is being let in continuously and the evaporator is collecting it.
Water under the crisper drawers, because all that extra moisture eventually melts during defrost and overwhelms the drain trough, or freezes the drain and finds another route.
A compartment that runs a degree or two warm at the door end while the far side is fine.
A door that needs a push to close properly, or that visibly stands off at one corner.
The paper test, and why it is not the whole answer
Close a strip of paper in the door and pull it out. Real resistance is a seal doing its job; a strip that slides freely is a seal that is not. Do it at several points around the door, especially at the corners and along the hinge side.
The reason it is not the whole answer is that a gasket can pass that test and still be poorly seated, or the door itself can be slightly out of alignment on a heavy built-in, or the cabinet the unit sits in can have moved. Beach houses move seasonally more than people expect, and a built-in that was set true five years ago may not be true now.
Alignment is usually adjustable. That is a satisfying repair, because the part count is zero.
What we check on a humidity call
Door seal condition and seating all the way around. Door alignment against the cabinet and against the other door. The perimeter heaters. The evaporator for frost pattern, which tells you how long air has been getting in. The drain trough and tube. Compartment temperatures at both ends.
Only then does anything get ordered. A gasket is not an expensive part, but a gasket fitted to a door that is out of alignment is a gasket that will fail in the same place again — and a sweating door on a genuinely humid coastal kitchen is sometimes just a kitchen doing what kitchens do here.