Sub-Zero Fridge Error Code SU: Unplugged Sensor... | appliancefaults.com

Technical Background:

The Sub-Zero's MCU (Main Control Unit) monitors the fridge temperature sensor. The sensor is a thermistor that changes resistance with temperature. The MCU sends a small DC voltage (typically 5V) through the sensor, and the voltage drop across the sensor is measured. If the sensor is unplugged, has a short, or is outside its acceptable resistance range, the MCU will trigger the SU error code.

Symptoms:

My Sub-Zero fridge is showing error code SU. The fridge seems warmer than usual, and the compressor is running constantly. I also noticed some ice buildup on the back wall of the fridge section.

Possible Causes:

Disconnected or damaged fridge temperature sensor
Faulty wiring harness connecting the sensor to the control board
Corroded or loose sensor connector pins
Defective main control board (MCU)
Sensor wires shorted to ground
Ice buildup around the sensor affecting readings

Solution:

1

Disconnect power to the Sub-Zero refrigerator at the breaker panel. Lock Out Tag Out (LOTO) procedures must be followed.
2

Locate the fridge temperature sensor, usually near the evaporator coil or in the fresh food compartment. Consult the service manual for the exact location.
3

Inspect the sensor wiring and connector for any visible damage, corrosion, or loose connections. Use a multimeter to check for continuity in the wiring.
4

Using a multimeter, measure the resistance of the temperature sensor. Compare the reading to the temperature/resistance chart in the service manual. A reading significantly outside the expected range indicates a faulty sensor.
5

If the wiring and sensor appear to be good, check the voltage at the sensor connector on the main control board. You should typically see around 5V DC. If there's no voltage, the control board may be faulty.
6

Replace the fridge temperature sensor if it is defective. Ensure the new sensor is properly connected and secured.
7

Reconnect power to the refrigerator and monitor for the error code. If the error code persists, the main control board may need replacement. Consider consulting a qualified technician.

Safety Warning:

Disconnect power to the appliance at the breaker panel before performing any repairs. High voltage is present within the appliance, and failure to disconnect power can result in serious injury or death. Always use proper Lock Out Tag Out (LOTO) procedures.

Prevention:

Regularly inspect the fridge's interior for excessive ice buildup. Ensure proper door sealing to prevent humidity from entering. Wipe down the interior regularly to prevent spills and food debris from accumulating. Check the door gasket and replace if damaged or cracked.

Expert Tip:

Some Sub-Zero models have a diagnostic mode. To enter diagnostic mode, press and hold the WARMEST and COLDEST buttons on the control panel simultaneously for 5 seconds. This will allow you to cycle through the various sensors and components and view their readings. Use the service manual to interpret the data.

Frequently Asked Questions

•What is the typical resistance range for a Sub-Zero fridge temperature sensor at 35°F?

The resistance will vary based on the specific sensor and model, but typically falls between 2.5k ohms and 5k ohms at 35°F. Consult the Sub-Zero service manual for your specific model.

•How do I test the continuity of the wiring harness?

Disconnect power to the refrigerator. Disconnect the wiring harness from both the sensor and the main control board. Use a multimeter set to continuity mode. Place one probe on one end of a wire and the other probe on the other end of the same wire. If the multimeter beeps or shows a low resistance (near 0 ohms), the wire has continuity. Repeat for each wire in the harness.

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

You can often find service manuals online by searching for your specific Sub-Zero model number followed by 'service manual' or 'technical guide'. Sub-Zero's website or authorized service providers might also provide access to these documents. They can also be purchased.

Sub-Zero Fridge Error Code SU: Unplugged Sensor Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•What is the typical resistance range for a Sub-Zero fridge temperature sensor at 35°F?

•How do I test the continuity of the wiring harness?

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

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: