Midea M-Thermal Arctic HT R290 Mono fault PP

What it means

Protection triggered when the temperature difference between outlet water (Twout) and inlet water (Twin) exceeds the threshold for a sustained period. In cooling mode: Twout-Twin>=3°C for 15 minutes. In heating/DHW mode: Twin-Twout>=3°C for 15 minutes.

Likely causes

1. Abnormal temperature difference between inlet and outlet water, typically indicating restricted/insufficient water flow or sensor fault
2. Outlet pipe and inlet pipe connected reversely
3. Tw_in sensor and Tw_out sensor connected reversely on plate heat exchanger or Main control PCB
4. Tw_out/Tw_in temperature sensor failure
5. Connection cable of 4-way valve disconnected or misconnected
6. Main Control PCB fault (no voltage output to 4-way valve port)
7. 4-way valve failure
8. Water temperature sensor resistance does not match expected characteristics table value
9. Unit capacity not matched to the system (oversized or undersized)
10. Heat exchanger coil in DHW tank too small (insufficient heat exchange area)
11. Insufficient water volume in system / high water side resistance due to lack of buffer tank
12. Loose, misconnected, broken or moisturized sensor connection
13. Sensor short-circuit (resistance < 0.5 kΩ)
14. Sensor failure (resistance > 380 kΩ)
15. Resistance inconsistent with resistance characteristics table
16. Sensor probe dislodged from installation position
17. Main Control PCB failure
18. Power supply is abnormal
19. Power supply abnormality

Where to start

1. Check Twout-Twin difference in cooling mode - should not be ≥3℃ for more than 15 mins
2. Check Twin-Twout difference in heating/DHW mode - should not be ≥3℃ for more than 15 mins
3. Check if outlet pipe and inlet pipe are connected reversely; re-connect securely if so