Fujitsu AUUH18LUAS Service Manual page 110

Check point 5. Check the refrigerant amount
Check the refrigerant leakage.
Check point 6. Replace the main PCB
If check point 1 to 5 do not improve the symptom, replace the main PCB.
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2-34. E: A3.↓. Compressor temperature error (Outdoor unit) 2. Troubleshooting with error code