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| Error Code | Fault Meaning & Symptoms | Suspected PCB Component | Diagnostic Action | Lab Repair |
|---|---|---|---|---|
| U4 | Daikin Inverter AC U4 Error Code PCB Repair Outdoor unit does not start; green LED on outdoor motherboard is dead or blinking 5 times; indoor fan runs with no cooling. | Outdoor Main Inverter Sub-PCB & Optocoupler Array | Check 24V communication loop, replace optocouplers (PC817 / TLP281), inspect communication resistors (20k ohm / 2W), replace outdoor MCU if line was struck by surge. | WhatsApp Repair Board |
| L5 | Daikin Inverter AC L5 Error Code Instantaneous Overcurrent Inverter compressor starts for 15-30 seconds then abruptly trips with L5 error on remote control. | High-power IPM Module (STK760-220A / PS219B4) | Desolder and test IGBT/IPM module with diode test on multimeter. Replace IPM module with genuine STK or Mitsubishi IGBT module, replace 450V electrolytic filter capacitor. | WhatsApp Repair Board |
| U4 | Daikin Inverter AC U4 Error Code PCB Repair Outdoor unit does not start; green LED on outdoor motherboard is dead or blinking 5 times; indoor fan runs with no cooling. | Outdoor Main Inverter Sub-PCB & Optocoupler Array | Check 24V communication loop, replace optocouplers (PC817 / TLP281), inspect communication resistors (20k ohm / 2W), replace outdoor MCU if line was struck by surge. | WhatsApp Repair Board |
| L5 | Daikin Inverter AC L5 Error Code Instantaneous Overcurrent Inverter compressor starts for 15-30 seconds then abruptly trips with L5 error on remote control. | High-power IPM Module (STK760-220A / PS219B4) | Desolder and test IGBT/IPM module with diode test on multimeter. Replace IPM module with genuine STK or Mitsubishi IGBT module, replace 450V electrolytic filter capacitor. | WhatsApp Repair Board |
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