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

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.