Common fault
Why does frost keep building up in my freezer?
Short answer
Ice that rebuilds within a week or two of being cleared is a defrost cycle that starts and never gets to the end of its job, and on this equipment the reason splits by the age of the unit.
What is actually going on
On the older built-ins the parts are mechanical: a defrost heater that has burned open, or a termination thermostat that no longer closes. On the board-managed columns the defrost is adaptive, scheduled from compressor run time and door openings, so a door switch that has stopped registering will keep a perfectly healthy heater from ever being called. The third cause is common to both, and it is the cheapest one: a door gasket whose magnet has gone weak, admitting more moisture each day than the cycle is able to take back out.
What we check, and in what order
The door switch is the one nobody looks at. On a column that schedules its own defrost, the control counts how often the door has been opened and how long the compressor has run, and it works out when a defrost is due from that. A switch stuck closed makes the unit believe the door is permanently open. A switch stuck open makes it believe the door is never opened at all, and the defrost interval stretches until the coil ices between cycles. Neither posts a code. It is found by watching whether the interior lighting and the evaporator fan respond correctly when the door moves, which takes ten seconds and gets skipped constantly.
On the mechanical side the tests are old-fashioned and quick. The heater is checked for continuity and for the current it actually draws, because a heater can read continuous and still be too weak to clear a coil. The termination thermostat either closes at its temperature or it does not. The thermistor is read as a resistance and compared with what the table says it should be at the temperature it is actually sitting in, since a sensor a few degrees out looks entirely plausible on the display and will hold off a defrost indefinitely.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
Reviews
The wine cabinet is built into the dining room millwork and the lower shelves had been drifting warm since spring. He left a probe down among the bottles instead of trusting the panel, and it was the fan in that zone. He also chased down a hum I'd learned to ignore.
- ★★★★★
We're off the gas main out past Escondido and run on propane, and the Wolf has browned unevenly since the day it was installed. Everyone who looked at it before said that's just how it cooks. He checked the conversion instead, and it had never been finished properly.
- ★★★★★
Water showed up at a floor seam several feet from the fridge. On slab it apparently travels sideways under the toe kick. It was the drain, and he poured water through afterwards to show it reaching the pan.
Appliance down in San Diego?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.
Questions
Frequently asked questions
Will you have to pull my built-in out of the cabinetry to work on it?
Almost never. A Sub-Zero built-in is meant to be serviced where it stands: the condenser and compressor deck through the grille, the evaporator behind a panel inside the compartment, the controls without disturbing the installation. Dragging one out of a tight opening risks the surround, the flooring and the custom panel. Sealed-system work is the exception, and you would hear about it first.