Sub-Zero Refrigerator Error Code 42: Defrost Cycle... | appliancefaults.com

Technical Background:

The Sub-Zero's MCU (Microcontroller Unit) monitors the defrost cycle. Error 42 indicates that the defrost heater failed to raise the evaporator coil temperature within a specified timeframe. The MCU controls a relay that supplies 120V AC to the defrost heater through the defrost thermostat.

Symptoms:

The homeowner notices excessive frost buildup in the freezer, leading to reduced cooling efficiency in both the freezer and refrigerator compartments. Ice may be visible on the back wall of the freezer, and food may not be freezing properly.

Possible Causes:

Defective defrost heater
Faulty defrost thermostat
Failed defrost timer or control board
Airflow obstructions causing excessive frost buildup
Wiring harness issue affecting the defrost circuit
Condenser coil blocked with dust.

Solution:

1

Disconnect power to the Sub-Zero refrigerator at the breaker panel (LOTO).
2

Locate the defrost heater, usually behind the evaporator coil inside the freezer section. Use a multimeter to test the heater for continuity. A reading of OL (open line) indicates a failed heater.
3

Check the defrost thermostat, which is typically wired in series with the heater. It should be closed (showing continuity) when cold. If open, replace the thermostat.
4

If the heater and thermostat test good, inspect the defrost timer or control board. For electronic boards, visually inspect for burned components.
5

Measure voltage at the defrost heater connection during the defrost cycle. You should see 120V AC. No voltage indicates a control board or wiring issue. Use a non-contact voltage tester before touching any wires.
6

Inspect the evaporator coil for excessive frost buildup. Ensure proper airflow by cleaning the condenser coils and checking the evaporator fan motor. Clean condenser with a brush or vacuum.
7

After repairs, monitor the refrigerator to ensure the defrost cycle is functioning correctly.

Safety Warning:

Always disconnect power to the appliance before performing any repairs. Use proper Lock-Out/Tag-Out (LOTO) procedures to prevent accidental re-energizing of the circuit. High voltage is present in the control panel and wiring harness.

Prevention:

Clean the condenser coils at least every six months using a brush or vacuum cleaner. Ensure proper door seals to prevent excessive moisture from entering the refrigerator. Avoid overpacking the freezer, which can restrict airflow.

Expert Tip:

Some Sub-Zero models have a service mode that allows you to manually initiate a defrost cycle for testing purposes. Consult the service manual for the specific sequence for your model. Usually involves pressing a specific set of buttons simultaneously.

Frequently Asked Questions

•How do I access the defrost heater in my Sub-Zero?

The defrost heater is typically located behind the rear panel inside the freezer compartment. You'll need to remove the shelves and any ice buildup to access the panel. Then remove the screws holding the panel in place. Be careful not to damage any wiring while removing the panel.

•What is the typical lifespan of a Sub-Zero defrost heater?

The lifespan of a Sub-Zero defrost heater can vary depending on usage and environmental conditions, but typically, it lasts between 5 to 10 years. Regular maintenance, such as cleaning the condenser coils, can help extend its lifespan.

•Can a faulty door seal cause Error Code 42?

Yes, a faulty door seal can contribute to Error Code 42. When the seal is compromised, warm, moist air enters the freezer, leading to excessive frost buildup on the evaporator coil. This increased frost can prevent the defrost cycle from completing within the allotted time, triggering the error.

Sub-Zero Refrigerator Error Code 42: Defrost Cycle Timeout Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•How do I access the defrost heater in my Sub-Zero?

•What is the typical lifespan of a Sub-Zero defrost heater?

•Can a faulty door seal cause Error Code 42?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: