Common fault
Why does frost keep building up in my freezer?
Short answer
Frost that comes back after you clear it means the automatic defrost is not finishing its cycle, and clearing it by hand treats the symptom while the cause carries on.
Why we start there
Three things account for nearly all of it: a defrost heater that has failed, a thermistor reading out of range so the cycle never triggers properly, or a door gasket whose magnet has gone weak, so the cabinet takes on moisture all day long and the cycle never gets ahead of it. Under a Carmel Valley marine layer that morning air is damp, and the last of the three moves faster here than owners expect.
What happens next
The ice itself is what does the damage. A coil furred with frost is insulated by it, so heat transfer drops, the compartment runs a little warmer every week, and the display goes on reporting the number it was asked to hold. Owners describe this as the freezer gradually getting worse rather than breaking, which is exactly what it is. By the time drawers are frozen into their runners, the coil has been struggling for months and the contents have been cycling through temperatures they should never have seen.
What we check, in order. Where the frost is: light and even across the back wall is humidity, a heavy pad in one area is defrost. Then the heater, for continuity. Then the thermistor, against its resistance curve at a known temperature. Then the drain, because a drain that iced closed usually iced for the same underlying reason. Then the seal, with a sheet of paper closed in the door at several points around the frame, top edge first. Integrated units get their door alignment checked at the same time, since a dropped door and a tired gasket look identical from the outside.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
Water was creeping out under the front edge onto engineered plank and I called at nearly ten at night in a panic about the floor. A person picked up, someone was out the next morning. Defrost drain iced closed, not the water line. He cleared it and dried underneath properly.
Fast, tidy, explained what he was doing. The hum carried across the whole open-plan downstairs and I could never place where it came from. Condenser fan bearing. Apparently a neighbor two doors along had the same part done a few weeks earlier, which on our street is not a coincidence.
Ours are the columns hidden behind cabinetry, so you see nothing until it misbehaves. Frost in one top corner and furry ice coming out of the maker. The door had settled under the panel weight and the seal only half met along the top. He measured it rather than guessing at the hinge.
Appliance down in Carmel Valley?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.
Questions
Answers before you call
Will a repair affect my Sub-Zero factory warranty?
Check with the manufacturer before you book anyone, ourselves included. Coverage on the sealed system turns on who did the work, so use a repair you already own before buying it twice. This comes up in the newer Pacific Highlands Ranch and Torrey Highlands kitchens, where equipment can still be young enough to be covered; built-ins in older Carmel Valley are well past it.