Midea M-Thermal Arctic HT R290 Mono fault BA

What it means

T4 sensor detected temperature outside of normal operation range. In heating/DHW mode, the error occurs when T4≥65℃ or T4<-25℃. In cooling mode, the error occurs when T4≥65℃ or T4<-5℃.

Likely causes

1. T4 sensor reading out of range
2. T4 sensor fault
3. Feedback signal cable CN17 not connected properly
4. Loose, misconnected, broken or moisturized sensor connection
5. Sensor short-circuit (resistance < 0.5 kΩ)
6. Sensor failure (resistance > 380 kΩ)
7. Resistance inconsistent with resistance characteristics table
8. Sensor probe dislodged from installation position
9. Main Control PCB failure
10. Pump stalling due to impeller obstruction

Where to start

1. Check CN17 connector for proper seating
2. Step 1: Check if temperature sensor connection on Main Control PCB is loose, misconnected, broken or moisturized. If yes, reconnect the temperature sensor correctly and keep it dry.
3. Step 2: If connection is fine, pull out the temperature sensor and measure sensor resistance. If resistance is too low (<0.5 kΩ), sensor has short-circuited. If resistance is too high (>380 kΩ), sensor has failed. Compare to the resistance characteristics table in Part 4 Appendix; if inconsistent, sensor has failed. Replace the sensor if so.