General Assist Technical Reference
LJBYL Outdoor Unit
Filter PCB reactor-coil overheating caused by incorrect wiring
Inspection and corrective-action guidance for field technicians
Field reports have identified LJBYL outdoor units where the reactor coil or Filter PCB overheats after operating for a period of time. The reported condition has been associated with incorrect reactor wiring at the Filter PCB terminal block.
Electrical hazard: The Filter PCB contains hazardous mains and DC-bus voltages. Testing and repairs must only be completed by appropriately licensed and qualified service personnel. Isolate power, apply lockout/tagout procedures and confirm that stored DC voltage has discharged before touching terminals or conductors.
1. Reported symptoms
- Reactor coil, terminal block or surrounding Filter PCB area becomes unusually hot.
- Visible discolouration, scorching, melted insulation or heat deformation near the reactor connections.
- Burning smell or electrical odour from the outdoor unit.
- Unit may operate normally initially and then stop after approximately 30 to 60 minutes.
- Protective shutdown, blown fuse or circuit-breaker operation may occur.
Do not continue operating the unit where heat damage, odour, melting or discolouration is present. Continued operation may cause further damage to the Filter PCB, reactor, wiring harness or connected power components.
2. Likely cause
The reported failure condition is caused by the reactor leads being connected to the incorrect terminals on the Filter PCB terminal block. This places the reactor outside its intended circuit path or applies current through an incorrect connection, resulting in excessive heating at the reactor, terminals or PCB tracks.
The reactor must be connected exactly as shown in the applicable LJBYL service manual, wiring diagram and PCB terminal markings. Do not rely on wire colour alone, as production revisions or replacement harnesses may vary.
Key principle: Both reactor leads must be fitted to the designated reactor terminals so that the reactor remains in the intended power-conversion circuit. Incorrect placement can create excessive current, high-resistance heating or abnormal loading of the Filter PCB.
3. Inspection procedure
- Isolate the outdoor unit. Switch off the supply at the isolator and upstream protective device.
- Confirm safe discharge. Wait the period specified in the service manual and verify that the DC bus has discharged before proceeding.
- Access the Filter PCB. Remove covers in accordance with the service manual.
- Inspect the reactor and terminals. Check for scorching, loose connectors, damaged locking tabs, melted housings, darkened copper, cracked solder joints or damaged PCB tracks.
- Check terminal location. Compare each reactor lead against the model-specific wiring diagram and terminal markings printed on the Filter PCB.
- Check connector engagement. Confirm that each connector is fully inserted, locked and not loose on the terminal.
- Inspect associated components. Examine the rectifier, relay, fuse, ACTPM/IPM area, harnesses and adjacent components for secondary heat damage.
| Inspection result | Required response |
|---|---|
| Incorrect wiring with no visible heat damage | Correct the wiring using the applicable schematic, inspect terminal tension and complete the verification procedure before returning the unit to service. |
| Discoloured or heat-damaged connector | Replace the damaged connector or harness and inspect the mating terminal and PCB for heat damage. |
| Burnt PCB, damaged track, melted terminal or damaged reactor | Replace the affected components. Do not attempt to reuse visibly heat-damaged electrical parts. |
| Secondary damage to rectifier, ACTPM/IPM or wiring | Complete full electrical diagnosis and replace all affected components before energising. |
4. Corrective action
- Confirm the exact outdoor-unit model and serial number.
- Obtain the correct service manual and wiring schematic for that production version.
- Reconnect the reactor leads to the designated Filter PCB terminals shown in the schematic.
- Replace the Filter PCB where there is evidence of burning, carbonisation, damaged tracks, melted terminals or compromised solder joints.
- Replace the reactor where the winding, insulation, lead terminals or connector housing has been heat damaged.
- Replace any damaged harness or connector. Do not repair heat-damaged high-current connectors with temporary terminals or non-approved joins.
- Confirm that all terminals are fully seated and secured. Apply only the fastening method and torque specified by the manufacturer.
- Reassemble all guards and covers before restoring power.
Important: Do not assume that replacing the Filter PCB alone will resolve the issue. The reactor wiring must be checked and corrected before the replacement board is energised, otherwise the new board may also be damaged.
5. Post-repair verification
- Complete continuity and insulation checks required by the service manual before restoring power.
- Confirm supply voltage and phase conditions are within specification.
- Start the unit and check for abnormal noise, odour, vibration or rapid temperature rise.
- Monitor the unit under load for at least 60 minutes where site conditions allow.
- Measure operating current and DC-bus voltage only at the approved test points and compare the readings with the service data for the model.
- Use a suitable non-contact temperature instrument to compare the repaired reactor, terminals and PCB area against adjacent components.
- Stop the unit immediately if temperature continues to rise, discolouration appears or an abnormal smell is detected.
- Record the final wiring position, measurements, replaced parts and test duration on the service report.
6. Preventive controls
- Photograph all high-current wiring before disconnecting the Filter PCB or reactor.
- Transfer one connector at a time when replacing a PCB.
- Match every connection to the PCB terminal marking and wiring diagram before energising.
- Do not use conductor colour as the sole method of identification.
- Inspect connector retention and signs of heat damage during commissioning and service visits.
- Escalate repeated failures with the model, serial number, PCB part number, photographs and operating measurements.
7. Diagnostic summary
| Condition | Likely issue | Action |
|---|---|---|
| Reactor or connector becomes hot | Incorrect connection, loose terminal or damaged contact | Isolate, inspect and correct wiring before further operation |
| PCB is scorched or carbonised | Sustained thermal or electrical damage | Replace PCB and inspect reactor and harness |
| Replacement board fails again | Original wiring fault or related component fault remains | Recheck wiring against schematic and test associated power components |
| Breaker or fuse operates | Short circuit or failed power component | Do not reset repeatedly; complete electrical diagnosis |
Reference: Field photographs supplied with this article show the LJBYL Filter PCB, reactor assembly and reactor-lead connections. Always use the current model-specific service manual and wiring diagram as the controlling technical reference.
