Sub-Zero Refrigerator Error Code 20 2 07

Error code 20 2 07 on a Sub-Zero refrigerator indicates a defrost bi-metal error. The bi-metal thermostat is a safety device located on the evaporator coil assembly that acts as a thermal cutout during the defrost cycle. It is wired in series with the defrost heater and is designed to open the circuit when the evaporator reaches a safe temperature, preventing overheating. When the control board detects that the bi-metal is not operating within expected parameters, such as remaining open when it should be closed, it logs this fault code.

The primary diagnostic step is to measure the resistance across the bi-metal thermostat. A properly functioning bi-metal in its closed state should read near zero ohms (continuity). An open reading at room temperature indicates a failed bi-metal that has tripped permanently or has failed open and will not reset. Since the bi-metal and defrost heater are wired in series, a failed or open-circuited defrost heater can also prevent the circuit from completing, which is why the service procedure directs technicians to check bi-metal ohms and replace the defrost heater if necessary.

Common root causes include a bi-metal that has failed due to repeated thermal stress, a defrost heater that has burned out and broken the series circuit, or wiring faults such as loose connectors or corrosion at the terminals connecting these components. Resolving this fault typically restores normal automatic defrost operation and prevents frost accumulation on the evaporator that would otherwise restrict airflow and reduce cooling performance.