Common fault
Why is my Sub-Zero refrigerator not cooling?
Short answer
Tell us which compartment is warm before anything else, because that one detail splits the job in half.
What is actually going on
A Sub-Zero built-in gives each compartment a sealed system of its own, so a freezer still holding hard ice has already cleared the costly half of the machine and leaves the refrigerator side to answer for it. Three parts do most of that answering: the evaporator fan on the refrigerator circuit, the defrost components that let its coil ice up behind the rear panel, and the thermistor telling the control what that compartment is actually doing. The second thing we need is the model number, because on an older unit that defrost is a heater, a termination thermostat and a timer, and on a recent integrated column it is a control board making the decision. Same symptom, two different repairs. If both compartments have climbed together, the conversation starts at the condenser instead.
What we check, and in what order
The model and serial plate is on the frame inside the door on most built-ins, and behind the lower grille on some PRO units. It is worth two minutes with a phone light, because it decides which parts leave the shop. On the older mechanical units we are testing a heater for continuity and current, and a termination thermostat that either closes at its temperature or does not. On the board-managed columns we put the unit into its service mode, read what the board believes the compartment is doing, and check that against a calibrated probe. A board that has been told the wrong temperature will run the wrong defrost schedule quite happily for months without posting a code.
Ice behind the rear panel looks like the fault and is almost always the consequence of one. Once a defrost cycle stops finishing, the coil builds a shell of ice, the shell acts as insulation, and less air gets through the compartment with every passing week. It is why owners report this one as a slow slide instead of a breakdown, and why the top shelf can be warm while the display still shows a perfectly reasonable number. Clearing the ice by hand will restore cooling for a few days and then it will come back, so treat it as a way to save the groceries, not as a repair.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
Reviews
I had started pricing new refrigerators. Ours is older than the remodel that went around it in this Mission Hills house, and the frost came back within a week every time I cleared it. He tested the heater and the thermostat rather than guessing. No frost since.
- ★★★★★
Two other outfits had been out to the Thermador freezer column and both wanted to replace the board. He moved the door and watched whether the light and fan responded, and the switch had quit, so the thing never scheduled a defrost. The fridge column beside it was fine all along.
- ★★★★★
Ice from the bar machine had gone small and hollow and I assumed the maker was finished. He measured what was actually reaching the valve before naming a part: scale in the screen, plus a filter well past its life. Nobody had told me the water here was that hard.
Appliance down in San Diego?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.