Carrier ComfortLink Alarm 31 – Supply Air Sensor Fault Explained

What Does Alarm 31 Mean?

Carrier ComfortLink Alarm 31 typically indicates a supply air temperature sensor out-of-range condition.

The system may:

• Disable cooling stages
• Enter protection mode
• Display unstable temperature readings

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Common Causes

• Failed thermistor
• Wiring open circuit
• Shorted sensor
• Moisture intrusion
• Improper sensor placement

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Troubleshooting

1. Measure sensor resistance
2. Compare to manufacturer temperature chart
3. Inspect wiring and terminals
4. Verify control board voltage reference

Replace sensor if readings are incorrect.

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FAQ

Is this similar to Alarm 42?
Yes, both relate to sensor input faults, though model specifics vary.