Sub-Zero Code 20 2 06: Mis-Wired Defrost Bi-Metal

Code 20 2 06 means the defrost bi-metal is mis-wired or improperly mounted, so the control saw abnormally high temperatures during defrost together with an inappropriate response from the bi-metal. Instead of reading a normal end-of-defrost signal, the board interprets the combination as a wiring or mounting fault and turns the SERVICE light on. The bi-metal that should sense and limit defrost heat is not connected or positioned to do its job.

Both are mis-wired or misplaced defrost bi-metal faults, but 20 2 06 fires with the SERVICE light on because evaporator temperatures actually climbed too high during defrost, while 20 2 05 logs quietly with normal in-range temperatures and no SERVICE light. So 20 2 06 is the more serious version where the heat got away before the bi-metal could respond.

The technician removes the evaporator cover and meters the circuit to verify bi-metal wiring polarity, terminal routing, and clip placement. They confirm the leads are not swapped or on the wrong terminals, the connector is tight and not corroded, the harness is not chafed or pinched, and the clip is seated on the evaporator tubing so the switch reads true coil temperature.

Owner-safe steps are confirming the displayed code, noting whether frost is building up, checking whether the unit had recent service that may have disturbed wiring, and making sure the freezer is not overloaded so air can reach the evaporator. Correcting the wiring polarity and clip placement requires opening the evaporator and metering the circuit, which a technician should perform.

This is a medium-urgency fault. The unit keeps cooling, but with the bi-metal not limiting defrost heat correctly you may see frost or ice on the evaporator and freezer walls, defrost cycles running too long, an unusually warm evaporator after defrost, and compartments drifting warmer over time. Schedule service before the defrost behavior worsens.

The fix is correcting the bi-metal wiring and remounting it against the evaporator; the defrost bi-metal (termination thermostat) is replaced if its sensing surface or clip is damaged, and the harness or connector is replaced if leads are chafed, corroded, or cannot hold a secure connection. We charge a flat $89 diagnostic, warranty the work 365 days, and you can call (650) 668-1554 to schedule.