Sub-Zero Refrigerator: Dual Compressors Not Turning On -... | appliancefaults.com

Technical Background:

MCU logic and voltage paths.

The Sub-Zero refrigerator uses a main control board (MCU) to manage compressor operation. The MCU monitors temperature sensors and other inputs to determine when to activate the compressors. When cooling is needed, the MCU sends a 120V AC signal to relays that switch power to the compressor start relays and overload protectors. These components then energize the compressor motor windings.

Symptoms:

US homeowner observations.

The Sub-Zero refrigerator is not cooling in either the refrigerator or freezer compartments. Both compressors are silent and not vibrating. The lights inside the refrigerator are working normally. No unusual noises or error codes are displayed.

Possible Causes:

Failed start relay or overload protector on one or both compressors.
Faulty compressor motor windings in either or both compressors.
Defective main control board (MCU) not sending voltage to the compressors.
Tripped breaker at the breaker panel.
Low voltage condition at the wall outlet.
Locked rotor condition in one or both compressors.

Solution:

1

Verify 120V AC power at the wall outlet using a multimeter. If no voltage, check the breaker panel for a tripped breaker. Reset if necessary.
2

Disconnect power to the refrigerator at the breaker panel. Access the compressor compartment at the rear of the unit.
3

Visually inspect the start relays and overload protectors on both compressors for signs of damage (burn marks, swelling). Replace if damaged.
4

Use a multimeter to test the compressor motor windings for continuity. A reading of infinity indicates an open winding and a failed compressor. Replace the compressor.
5

Locate the main control board (MCU). Using the wiring diagram, identify the compressor relay outputs. With the refrigerator powered on (carefully), use a multimeter to check for 120V AC at the relay outputs when the compressors should be running.
6

If there is no voltage at the relay outputs, the MCU is likely faulty and needs replacement.
7

After replacing any components, verify proper compressor operation and cooling.

Safety Warning:

LOTO and high voltage warning.

Always disconnect power to the refrigerator at the breaker panel before performing any repairs. Use proper lockout/tagout (LOTO) procedures to prevent accidental re-energization. High voltage is present in the compressor compartment and at the main control board. Exercise extreme caution when working with electrical components.

Prevention:

Specific maintenance.

Clean the condenser coils at least every 6 months using a vacuum cleaner with a brush attachment. Ensure proper ventilation around the refrigerator. Avoid overloading the refrigerator, as this can strain the cooling system.

Expert Tip:

Trade secret or service mode sequence.

Many Sub-Zero models have a service mode that allows you to run diagnostics and test individual components. The service mode sequence varies depending on the model, but typically involves pressing a combination of buttons on the control panel. Consult the service manual for the specific sequence for your model. This can help pinpoint the exact cause of the compressor failure.

Follow-up Questions: 3 relevant technical questions a user might ask next.

Frequently Asked Questions

•What are the typical resistance readings I should see when testing the compressor windings?

Typical compressor winding resistance readings are between 2-10 ohms for each winding. Consult the service manual for specific values for your model. Significant deviation or an open circuit indicates a failed winding.

•How do I identify the correct replacement start relay and overload protector for my compressor?

The start relay and overload protector will have part numbers printed on them. You can use these numbers to order replacements. Alternatively, provide the refrigerator model number and compressor model number to an appliance parts supplier to find compatible replacements.

•Where can I find the service manual for my Sub-Zero refrigerator?

You can often find the service manual on the Sub-Zero website or by searching online using your refrigerator's model number. Some online appliance parts retailers also offer access to service manuals.

Sub-Zero Refrigerator: Dual Compressors Not Turning On - Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•What are the typical resistance readings I should see when testing the compressor windings?

•How do I identify the correct replacement start relay and overload protector for my compressor?

•Where can I find the service manual for my Sub-Zero refrigerator?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: