Sub-Zero Freezer Thermistor or Control Regulation Issue

Freezer temperature fluctuates; ice cream soft, then hard; compressor cycles seem irregular.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Aging or drifting freezer thermistor, Loose thermistor connection, Control board temperature regulation fault, Evaporator fan intermittent operation

How to Fix / Troubleshooting

Safety first: Disconnect power before accessing sensors or fans.

Step 1 – Verify with a thermometer

  • Place a thermometer in the freezer and log temperature over several hours.
  • Large swings (e.g., from 0°F to 20°F) suggest control or sensor issues.

Step 2 – Inspect and test freezer thermistor

  • Locate the freezer thermistor and ensure it is properly mounted.
  • Disconnect and measure resistance; compare to the temperature‑resistance chart.
  • Replace the thermistor if readings are unstable or out of spec.

Step 3 – Check evaporator fan

  • Confirm the freezer evaporator fan runs consistently when the compressor is on.
  • Replace the evaporator fan motor if it is intermittent or noisy.

Step 4 – Control board evaluation

  • If thermistor and fan are good but temperature swings persist, the main control board may be misregulating and should be evaluated by a technician.
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Repair Difficulty

Medium 3/5

Required Part

Freezer Thermistor
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