Sub-Zero Refrigerator Error Code 20 2 00

Error code 20 2 00 on a Sub-Zero refrigerator indicates that the defrost bi-metal thermostat is stuck in the open position. The bi-metal thermostat is a thermal cutout device positioned in the defrost circuit, typically mounted near the evaporator coil. Its job is to act as a safety limit: it closes to allow defrost heater operation when temperatures are low enough, and opens to cut power to the heater once the coil reaches a safe threshold temperature. When this component is stuck open, it prevents the defrost heater from receiving power at all, even when the evaporator is heavily frosted and a defrost cycle is needed.

The core diagnostic criterion for this fault is that the bi-metal reads as an open circuit when measured below -2 degrees Celsius. At that temperature, a properly functioning bi-metal should be closed, presenting continuity across its terminals. If an ohmmeter shows no continuity at or below that threshold, the bi-metal has either tripped without resetting or has failed permanently in the open state. A tripped bi-metal can sometimes be the result of a prior overtemperature event, such as a failed defrost heater that caused excessive heat buildup, or it may simply have reached the end of its service life.

When this fault persists, frost accumulates on the evaporator coil without being cleared, eventually restricting airflow through the refrigerator and freezer compartments. This leads to rising cabinet temperatures, compressor overrun, and potential food loss. Resolving the fault requires confirming the open-circuit condition under the specified temperature condition and replacing the bi-metal thermostat if it does not recover continuity after the evaporator has been allowed to fully defrost and cool back down.