Sub-Zero Refrigerator Error Code 71: Ambient Sensor... | appliancefaults.com

Technical Background:

error code 71 indicates the main control unit (MCU) has detected an open circuit in the ambient temperature sensor circuit. The MCU sends a small DC voltage (typically 5V DC) through a resistor and then through the thermistor (ambient temperature sensor). The thermistor's resistance changes with temperature, creating a voltage divider. The MCU monitors this voltage to determine ambient temperature. An open circuit means the MCU sees no voltage return from the sensor.

Symptoms:

The Sub-Zero refrigerator displays error code 71. The refrigerator may not maintain proper temperature. The unit may run continuously or not at all.

Possible Causes:

Faulty ambient temperature sensor
Wiring harness damage (open circuit)
Loose connection at the sensor or control board
Corroded terminals on the sensor or connector
Failure of the main control board (MCU)
Rodent damage to wiring

Solution:

1

Disconnect power to the Sub-Zero at the breaker panel.
2

Locate the ambient temperature sensor, typically near the top of the refrigerator compartment.
3

Visually inspect the sensor wiring and connections for damage or corrosion.
4

Using a multimeter, measure the resistance of the ambient temperature sensor. An open circuit indicates a faulty sensor. A good sensor will have a resistance value that varies with temperature. Consult the service manual for the correct resistance value at a given temperature (e.g., at 70°F, resistance should be approximately X ohms).
5

If the sensor is good, check the wiring harness for continuity from the sensor to the main control board using your multimeter. Look for breaks in the wire.
6

If the wiring is intact, inspect the connector at the main control board for corrosion or loose pins.
7

If all wiring and connections are good, the main control board may be faulty and require replacement.

Safety Warning:

Disconnect power to the appliance at the breaker panel before performing any repairs. Lock Out/Tag Out (LOTO) procedures should be followed. Some components may retain a high voltage charge even after the unit is unplugged. Consult a qualified technician if you are not comfortable performing these repairs.

Prevention:

Periodically inspect the refrigerator's wiring and connections for signs of damage or corrosion. Keep the area around the refrigerator clean to prevent rodent infestation.

Expert Tip:

After replacing the sensor or control board, clear the error code from the unit's memory. This is often done by pressing and holding specific buttons on the control panel for a certain duration, or by entering a service mode using a specific sequence. Consult the service manual for the exact procedure for your model. Some models require the unit to be powered off for several minutes to reset properly.

Frequently Asked Questions

•What is the typical resistance value of the ambient temperature sensor at room temperature (70°F)?

The resistance value varies depending on the specific Sub-Zero model, but a typical value is around 5000-10000 ohms at 70°F. Consult the service manual for your model to confirm the correct value.

•How do I access the main control board on my Sub-Zero refrigerator?

The location of the main control board varies by model. Typically, it's located behind an access panel at the top or rear of the refrigerator. You may need to remove screws and panels to access it. Always disconnect power before accessing any internal components.

•If the wiring appears to be damaged by rodents, what type of wire should I use to repair it?

Use appliance-grade wire of the same gauge (thickness) as the original wiring. Appliance-grade wire is typically high-temperature rated and resistant to moisture and chemicals. Ensure all splices are properly insulated with heat shrink tubing or electrical tape.

Sub-Zero Refrigerator Error Code 71: Ambient Sensor Troubleshooting

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip:

Frequently Asked Questions

•What is the typical resistance value of the ambient temperature sensor at room temperature (70°F)?

•How do I access the main control board on my Sub-Zero refrigerator?

•If the wiring appears to be damaged by rodents, what type of wire should I use to repair it?

Related questions

Technical Background:

Symptoms:

Possible Causes:

Solution:

Safety Warning:

Prevention:

Expert Tip: