Overview

Three-phase outdoor units operate differently from single-phase systems due to their PFC (Power Factor Correction) PCB and Active Converter Technology Power Module (ACTPM).
The PFC PCB is a critical component that manages current draw balance and power efficiency.
When faulty, it commonly results in circuit breaker tripping immediately upon energizing the system.

This procedure applies to:

  • Models: AOTDLATT, AOTDLBTT, AOTGLATT

  • PCB type: PFC (Power Factor Correction Board)

1. Common Symptoms of PFC PCB Failure

  • Main power breaker trips when unit is energized.

  • No power indication or immediate shutdown after power-up.

  • Possible burnt smell or visible board damage around high-current components.

⚠️ If the system trips on power-up without compressor engagement, the PFC board is the most likely cause.

2. Required Tools

  • Digital multimeter with diode test function.

  • Insulated probes suitable for PCB testing.

  • Correct wiring diagram or service schematic for reference.

3. Test Setup and Safety

  1. Isolate Power: Disconnect the air conditioner completely from mains supply.

  2. Access PCB: Open the outdoor unit and locate the PFC board (refer to diagram, page 1 of the guide).

  3. Identify Test Points:

    • TM504 (Orange) → Positive terminal

    • TM505 (Purple) → Negative terminal

    • TM500, TM501, TM502 → Intermediate test points used for circuit verification

Refer to page 1 image of the provided guide showing test point color coding and probe placements

PFC testing

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4. Testing Procedure

Using the multimeter in diode mode, perform the following tests between the listed terminal pairs:

Red Lead (+)Black Lead (–)Expected Reading (V)Result Interpretation
TM504TM500OLNormal
TM504TM501OLNormal
TM504TM502OLNormal
TM505TM5000.4Normal
TM505TM5010.4Normal
TM505TM5020.4Normal
TM501TM5040.4Normal
TM502TM5040.4Normal
TM505TM504OLNormal
TM502TM505OLNormal

Acceptable Range: Readings between 0.3 V and 0.5 V on diode scale are considered healthy junctions.
Failure Condition: If any test returns 0.0 V, the PCB is shorted and must be replaced.

5. Test Interpretation

  • All readings normal (0.4 V / OL): PCB is functional.

  • 0.0 V reading (short): Internal diode or transistor failure – replace PFC PCB.

  • Open circuit on all tests: Check for disconnected harness or blown board fuse before replacing PCB.

6. Service Notes

  • Testing the PFC PCB is similar to testing the IPM (Inverter Power Module), but the presence of choke coils introduces added resistance—expect slight measurement variation.

  • Always perform testing with complete discharge of the board’s capacitors to avoid false readings.

  • If the PFC is faulty, replace as a complete assembly; component-level repair is not recommended.

7. Technician Advisory

  • PFC failures are most often caused by:

    • Power surges or unbalanced supply voltage.

    • Moisture ingress or carbon tracking on PCB surface.

    • Compressor or IPM faults backfeeding current through the PFC.

After replacement, ensure correct earthing and surge protection to prevent recurrence.