Thermostat displays E3 and outdoor temperature shows -- or is clearly wrong

Safety first: Turn off power to both indoor and outdoor units at the breakers before working on wiring.

• Step 1 – Locate outdoor sensor: Find the iComfort outdoor temperature sensor, usually mounted near the outdoor condenser or integrated into the outdoor unit control board.
• Step 2 – Inspect wiring: Follow the sensor wires from the probe to the outdoor unit and then to the thermostat or equipment interface module. Look for cuts, abrasions, or rodent damage.
• Step 3 – Check connections: Tighten any loose terminal screws and clean corrosion from terminals using a small wire brush. Ensure the sensor wires are on the correct terminals as per the iComfort wiring diagram.
• Step 4 – Measure resistance: Disconnect the sensor and measure its resistance with a multimeter. Compare to the manufacturer’s temperature/resistance chart. Infinite or zero resistance indicates a failed sensor.
• Step 5 – Replace sensor: If the sensor is out of spec, install a new iComfort outdoor temperature sensor. Route the cable away from high‑voltage lines to reduce interference.
• Step 6 – Restore power and test: Turn power back on and verify that E3 clears and the outdoor temperature reading is reasonable.