Common fault
Why is my Sub-Zero refrigerator not cooling?
Short answer
Downtown the answer is usually heat, not refrigeration.
The reasoning behind that
A built-in rejects heat through its grille into a kitchen that often has no window and no exterior wall, so a coil packed with lint holds the cabinet a few degrees warm through the afternoon and lets it recover overnight. If the freezer is still hard-frozen while the refrigerator has climbed, that rules out the expensive answer on its own: these units run two separate sealed systems, and the working one proves the equipment can still make cold. What is left on the refrigerator side is its own evaporator fan or a defrost fault icing its coil. Both are ordinary parts and usually a one-visit repair.
How the diagnosis goes
What we check, in this order. First the grille and the condenser, because in an interior kitchen that is the single most likely cause and the cheapest to correct. Then the ambient at the grille itself, since a unit boxed into cabinetry with the discharge blocked is being asked to do something it cannot. Then the refrigerator-side evaporator fan, by ear and by hand at the vents, because a stopped fan leaves you with a cold coil and a warm cabinet. Then the defrost heater and the thermistor. Gauges come out only when those have been eliminated.
What is worth doing before we arrive. Take a real thermometer and put it on the middle shelf for an hour rather than trusting the panel, and open the freezer to see whether it is genuinely still frozen solid. Check that nothing is blocking the grille, at the top or the bottom depending on the model. Note whether the problem is all day or only from mid-afternoon onward, because a daily rhythm points straight at heat rejection and tells us what to bring. And keep the doors shut while you wait, however tempting it is to check.
If that matches what yours is doing, say so when you call — it decides which parts come on the van.
Ice had gone small and hollow right before a convention week with people staying with us. He put a gauge on the water line, said the pressure that far up the building was marginal and the filter was two years old. New filter and the cubes came out full the next day.
Our wine cabinet stands out in the living space against the glass and it was losing a few degrees every afternoon while the panel still read what I set. He measured down at the bottles, cleared the grille where it was breathing into the island, remeasured. No part, and he said so plainly.
Water on the floor of the loft and all I could think about was the ceiling of the unit under us. Same day, defrost drain iced shut, flushed it and checked the heater. Nothing got past the towels.
Appliance down in Downtown San Diego?
Tell us the brand and what it is doing — we can usually name the likely repair before we arrive.
Questions
Answers before you call
Is a built-in worth repairing, or should I replace it in a downtown condo?
Repairing usually wins, and in a high-rise it wins by more. Replacing an integrated column is not swapping a box: it means matching an exact cabinet opening, remaking or reusing a custom panel front, and getting the new unit through a corridor the original passed before the millwork was finished around it. The faults we actually see are ordinary parts.