The short answer
A cabinet that runs continuously and still warms up has lost airflow far more often than it has lost refrigerant. The compressor is working; something is stopping the cold it makes from reaching the food. Listen at the freezer with the door open and the light switch held in. Hearing the evaporator fan separates an airflow fault from a fan fault before anything is opened. On a Sub-Zero refrigerator the cause that ranks first is defrost cycle stalled, evaporator iced over.
What you observe
- The cabinet is warm but the compressor is clearly running — Cold is being made; it is not reaching the food.
- A solid sheet of frost on the freezer rear panel — The defrost system has stopped clearing the coil.
- The freezer is cold but the refrigerator is not — Airflow between the two compartments has stopped.
- NEAR MISS — the cabinet is silent and nothing is cold — That is a power or start-relay fault and it is a different page.
Causes, most likely first on a Sub-Zero refrigerator
- Defrost cycle stalled, evaporator iced over — The heater or its control stops clearing the coil, frost builds into a solid sheet behind the freezer panel, and air stops moving while the compressor runs on. It ranks first on a Sub-Zero refrigerator because a built-in installation breathes through a narrow cabinet cut-out, so anything airflow-related surfaces here long before it would on a free-standing machine.
- Condenser coil blanketed in dust — The coil rejects the heat the compressor removes, and once it is covered the machine runs continuously without ever getting the cabinet down. Second on this platform: a shallow plinth or a tight cut-out fouls a coil far faster than an open back does.
- Damper or air diffuser stuck — On a single-evaporator cabinet a flap meters cold air into the fresh-food side, and a stuck flap starves that side while the freezer stays fine. Last, and the reason to work down the list rather than guess: it mimics a failed fan exactly, so the fan has to be heard before this is considered.
Check in this order, and why
- Empty the freezer and look at the rear panel for a sheet of frost — A solid sheet rather than a dusting settles it immediately.
- Feel the coil area at the back or in the plinth for heat and dust — A thick dust blanket is visible and it is the cheapest fix here.
- Hold a tissue at the fresh-food vent with the door briefly open — Air arriving there rules the damper out; still air with a running fan points straight at it.
What an owner can safely check
- Empty the cabinet, switch it off and leave both doors open for a full defrost — Cold restored afterwards confirms the defrost system as the cause.
Tools: towelsAbout 45 min
- Unplug the cabinet and vacuum the condenser coil and its grille thoroughly — Do this twice a year on a compact or built-in cabinet, more with pets.
Tools: vacuum, soft brushAbout 25 min
- Check the gasket grips paper all the way round and clean the sealing face — Also check the cabinet is tipped slightly back so doors self-close.
Tools: cloth, paperAbout 15 min
- STOP HERE if the next step needs a meter on live terminals or a panel off — That is where an owner check ends and a service call begins, whatever the ranking above says.
Before you open anything
Safety
Unplug the cabinet or switch off its breaker before removing any interior panel — a capacitor can hold a charge after the power is off. Never cut, open or attempt to recharge a sealed refrigerant line.
When to call a technician
Call once the defrost, the coil, the door and the fan are all clean and the cabinet still runs warm: what is left is the sealed system, and refrigerant work is licensed work. On a cabinet of this class, insist the cause is named before any part is ordered: the parts are expensive enough that a guess is not worth making.
Nearest pages of this class
What this page does not cover
This page is written for the Sub-Zero refrigerator as a class, not for one family or model line. Where a family- or model-specific page exists for your unit it is linked above, it is the more specific answer, and it is the one to read first. Deliberately not here: part numbers, wiring colours, panel removal order and torque figures, all of which differ between families under the same nameplate.
Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
