E12
Carrier Outdoor Temperature Sensor Fault

Thermostat displays E12 and may show incorrect outdoor temperature or fail to optimize heat pump operation.

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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

Failed Carrier outdoor temperature sensor, Broken or shorted sensor wiring, Sensor mounted in direct sunlight or near exhaust, Loose sensor connection at furnace/air handler control board

How to Fix / Troubleshooting

Safety first: Turn off power to the HVAC system at the breaker before working on sensor wiring.

  • Step 1 – Locate sensor: Find the Carrier outdoor temperature sensor, typically mounted on the north or shaded side of the house near the outdoor unit.
  • Step 2 – Inspect mounting and location: Ensure the sensor is not in direct sunlight, near dryer vents, or other heat sources. Relocate if necessary.
  • Step 3 – Check wiring: Inspect the two-conductor cable from the sensor back to the furnace/air handler control board. Look for cuts, corrosion, or loose connections at the board terminals.
  • Step 4 – Test sensor resistance (advanced): With power off and sensor wires disconnected, measure resistance across the sensor leads and compare to Carrier's temperature/resistance chart. If readings are out of range, replace the sensor.
  • Step 5 – Replace sensor: Install a new Carrier outdoor temperature sensor, connect wires securely, and restore power. Verify that the thermostat now displays a reasonable outdoor temperature.
  • When to call a pro: If you cannot access the control board or do not have the resistance chart, have a Carrier technician test and replace the sensor.
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Repair Difficulty

Medium 3/5

Required Part

Carrier Outdoor Temperature Sensor
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