Common fault
Why does frost keep building up in my freezer?
Short answer
Frost that comes back after you have cleared it means the automatic defrost is not completing.
Why that is usually the answer
On a Sub-Zero the usual causes are a defrost heater that has failed open, a thermistor that has drifted far enough that the cycle never triggers, or a door gasket whose magnet has gone weak, so it admits humid air around the clock. The unit does not stop, it degrades. Ice on the evaporator insulates the coil, airflow falls away, and the number on the display stops matching the temperature around the food.
Where it usually turns out to be
Gaskets are the first thing we look at on the coastal strip and the last thing owners suspect. A built-in door in Dana Point or San Clemente closes against air that carries the marine layer for a good part of the year, so a gasket that has taken a set, cracked at a corner or lost magnet strength admits far more moisture here than the identical gasket would inland. Close the door on a dollar bill and pull it out. Where it slides free with no drag, the seal is not sealing. That test takes a minute and it explains a large share of the frost we get called about between the harbor and Talega.
If the gasket is sound, the defrost circuit goes on the meter. The heater is checked for continuity, the thermistor is checked against its resistance curve at a known temperature rather than by feel, and the control is confirmed to be calling for a defrost in the first place. Then the coil is cleared with heat and time, never with a screwdriver, because a punctured evaporator turns a routine repair into a sealed system job and that is the one mistake on this appliance nobody can take back.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
Called on a Sunday night about water pooling under the built-in and someone actually picked up. Next morning he found the drain iced shut, cleared it properly, and put a level across the cabinet because it had tipped forward over the years. Ran the dispenser before he left.
The wine cabinet we put in during the remodel held its top zone and crept up on the bottom one all summer. Two other outfits had been out and both wanted to sell me a board. He took the reading down at bottle level and it was the fan in that zone.
Cubes came out short and hollow all through August, and with people in and out of the house from the beach we go through a lot of ice. It was the filter cartridge and ice forming in the fill tube. He stayed and watched a whole batch drop before leaving.
Appliance down in Orange County?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.
Questions
Answers before you call
Why does the undercounter unit in the island fail when the main refrigerator is fine?
It sits in the least forgiving spot. Undercounter refrigerators, wine cabinets and ice machines reject heat forward through a narrow grille into a toe kick. In the newer inland houses in Talega, Ladera Ranch and Coto de Caza they complain first through a hot summer, usually from a closed-up condenser or a rug blocking the grille. We check coil and airflow before quoting anything electronic.