Indoor unit displays E3; unit may stop during heating or defrost cycles.

Safety: Turn off power at the breaker. Wait several minutes for capacitors to discharge before touching the PCB.

Steps:

• 1. Access coil area: Remove front cover and filters. Remove screws to expose the evaporator coil and sensor wiring.
• 2. Identify defrost/frost sensor: Some Airwell models use a separate NTC on the coil specifically for frost detection, often clipped near the lower part of the coil or drain pan area.
• 3. Check mounting: Ensure the sensor is firmly clipped to the coil or bracket as designed. If it has fallen into the drain pan or is hanging, reposition and secure it.
• 4. Inspect harness: Follow the sensor wires back to the indoor PCB. Look for broken insulation, corrosion, or loose connectors. Reseat the connector.
• 5. Measure resistance: Disconnect the sensor and measure resistance at room temperature. Compare with other NTC sensors in the unit; values should be similar. Replace if open/shorted or far out of range.
• 6. Replace sensor if needed: Install a new Airwell frost/defrost sensor of the same type. Clip it in the same location and route wires away from moving parts and sharp edges.
• 7. PCB evaluation: If sensor and wiring are good, the indoor PCB may misread the sensor. Look for burn marks or corrosion. PCB replacement is typically a technician job.
• 8. Test: Reassemble, restore power, and test in heating mode. Confirm E3 is cleared.