Sub-Zero not holding temperature
Sealed system
A cabinet that drifts a few degrees and will not come back. Read against the sensor and put on gauges before anything is named as the fault.
Thermistors
Control board
Charge check
Sub-Zero fridge warm but freezer cold
Airflow
Two separate sealed systems, so one side can fail while the other holds rock solid. Usually that side’s evaporator, its fan or the defrost circuit.
Evaporator fan
Defrost circuit
Air damper
Sub-Zero sealed system or refrigerant leak
Sealed system
The expensive end, and the one worth proving rather than guessing. Leak traced, repaired and recharged to the original specification.
Leak trace
Filter drier
Recharge
Sub-Zero freezer frost build-up
Defrost
Frost on the back wall points at the defrost heater, its bimetal or the control — or at a door seal letting humid room air in.
Defrost heater
Bimetal
Door gasket
Sub-Zero running constantly
Condenser
A condenser packed with dust, or a fan that has stopped. On a built-in all the heat leaves through the top grille, so a blocked one is fatal.
Condenser clean
Condenser fan
Grille airflow
Sub-Zero cycling on and off
Controls
Short-cycling is usually the start relay, the overload, or a board calling for cooling the sealed system cannot deliver.
Start relay
Overload
Control board
Sub-Zero compressor not running
Sealed system
Start relay, overload, or the compressor itself. The relay is the cheapest of the three and gets ruled in or out first, because that is the honest order.
Start relay
Overload
Compressor test
Sub-Zero ice maker leaking or overflowing
Water
Water supply before module. The inlet valve, the fill tube and pressure at the saddle valve account for most of these.
Inlet valve
Fill tube
Water line
Sub-Zero ice maker freezing over
Water
A fill tube frozen shut, or a harvest cycle that is not completing. These modules get replaced far more often than they have actually failed.
Fill tube heater
Harvest cycle
Module test
Sub-Zero water dispenser not working
Water
Dispenser switch, inlet valve, or a line frozen inside the door. The door is where most of these faults live.
Dispenser switch
Inlet valve
Door line
Sub-Zero wine cabinet not cooling
Wine storage
Two or three degrees off a set point is usually the zone sensor, the damper or the evaporator fan rather than the compressor.
Zone sensor
Damper
Evaporator fan
Sub-Zero display or control panel dead
Electronics
Read, not guessed. Some indicators are scheduled reminders rather than faults, and a code narrows it to a circuit that still has to be proven.
Fault codes
Control board
Harness