Midea M-Thermal Arctic HT R290 Mono fault P4

What it means

Protects the compressor from abnormally high discharge temperatures and transient spikes. Triggered when discharge temperature rises above 115°C.

Likely causes

1. Faulty Tp discharge temperature sensor
2. Tw_in/Tw_out sensor dislodged from installation port
3. Faulty Tw_in or Tw_out temperature sensor
4. Refrigerant leakage
5. Abnormally high discharge temperature
6. Transient temperature spikes in the compressor discharge line
7. Abnormal state detected requiring compressor protection
8. Set temperature reached (normal stop)
9. Abnormal system state detected

Where to start

1. Monitor discharge temperature (Tp) and suction temperature (Th) during compressor operation
2. Track compressor running time against 12 minute threshold for EA logic
3. If sensors are correctly installed, pull out Tw_out/Tw_in sensor from plate heat exchanger, leave it in the air for 10 mins; if the temperature difference between sensor and air is greater than 5°C, the sensor failed. Alternatively measure resistance and compare with sensor's resistance characteristics table (Appendix 4); if not consistent, the sensor has failed.