Most likely causes, in the order we check them
| Cause | What you see | Fix |
|---|---|---|
| Dirty condenser | Unit runs constantly, top of the cabinet feels hot, temperature slowly climbs. Sub-Zero asks for a condenser cleaning every 6-12 months. | You or us |
| Condenser fan failed | Compressor runs but heat is never carried away. Often a buzzing or silence where a fan should be heard behind the grille. | Technician |
| Evaporator fan failed | Freezer stays cold, fresh-food side goes warm. Cold air is made but never moved into the compartment. | Technician |
| Defrost fault | Evaporator turns into a block of ice, airflow stops. Cause is a defrost heater, thermistor or control board, not the ice itself. | Technician |
| Door gasket or alignment | Warm humid air is pulled in every hour. Common on heavy custom-panel doors that have dropped over the years. | You or us |
| Sealed-system leak | Cooling fades over weeks, compressor runs non-stop. Needs leak detection, evacuation and recharge - certified work, not a part swap. | Technician |
| Control board or sensor | Display shows a temperature the compartment does not actually hold, or the unit ignores the setpoint entirely. | Technician |
What you can safely check yourself
- The setting. Confirm the fresh-food side is set to 38°F and the freezer to 0°F, and that no one bumped the controls or left the unit in showroom or sabbath mode.
- The grille and the condenser. Pull the upper grille and vacuum the condenser coil. In coastal homes with pets this alone fixes a surprising number of calls.
- Airflow inside. Boxes pushed against the back wall or a full freezer basket can block the vents that feed cold air to the fresh-food side.
- The door. Close it on a dollar bill and pull. If the bill slides out with no resistance anywhere along the seal, the gasket is done.
- How long it has been warm. Note when it started and whether both sides are affected - it is the single most useful thing you can tell the technician on the phone.
One side cold, one side warm - what that means
Most built-in Sub-Zero refrigerators run dual refrigeration: the freezer and the fresh-food compartment each have their own sealed system. It is why food does not taste of the freezer, and it is also why half the appliance can fail on its own.
If the freezer is holding 0°F and the refrigerator is at 50°F, the freezer's system is fine. The fault is in the fresh-food side: its evaporator fan, its defrost circuit, or its sealed system. Nobody needs to replace the appliance because of it.
If both compartments are warm at once, look first at things they share - power, the condenser, the condenser fan, or a control board.
How long you have before food is at risk
A closed refrigerator holds a safe temperature for about four hours; a full freezer for around 48 hours, half-full for 24. Keeping the doors shut buys you most of that.
Practical order: move what you cannot replace to a cooler or a neighbour's freezer, keep the doors closed, and book the visit. Do not refreeze anything that has warmed above 40°F.
What the visit looks like
We measure rather than guess: temperatures at both evaporators, condition of the condenser, current draw on the fans, the defrost circuit, and pressures only if the sealed system is genuinely suspect. You get the cause and the price before any work starts.
Fans, gaskets, thermistors and water valves are on the van, so a large share of these calls finish in one visit. Anything model-specific is ordered as genuine Sub-Zero stock against your serial number.
Related Sub-Zero problems
Questions we get asked
How long should a Sub-Zero take to cool back down after a repair?
Expect 12 to 24 hours for a built-in unit to settle at temperature after the fault is fixed, longer if it was fully defrosted first. A unit that is still warm after a day has a second problem.
Is a Sub-Zero that runs constantly always broken?
Not always, but it is a warning. These compressors are designed to cycle. Constant running usually means the unit cannot reject heat - a dirty condenser, a dead condenser fan, or a low charge - and it is what eventually kills the compressor.
Can I just add refrigerant to fix it?
No. A sealed system does not consume refrigerant, so a low charge means a leak. Topping it up without finding the leak sends the same money out of the same hole, and refrigerant handling is restricted to certified technicians.
The refrigerator is warm but the light and display work. Is that better or worse?
It rules out a power problem and points at cooling: a fan, the defrost circuit or the sealed system. A dark display with no cooling at all is a different, usually cheaper, family of faults.