General Assist Technical Reference
Communication Test with Fan and Compressor Checks
Indoor-to-outdoor communication fault diagnosis
A communication error occurs when either the indoor unit or outdoor unit stops communicating with the other. The checks below are intended to help identify which side of the system has stopped transmitting and then narrow the fault to the relevant power, fan or compressor-control circuit.
DANGER – LIVE ELECTRICAL TESTING: Some of the checks in this procedure require the system to be energised. Live testing must only be carried out by appropriately licensed and competent service personnel using suitable test equipment and safe work practices. Isolate power before disconnecting or reconnecting wiring.
1. Confirm the power supply
Before investigating the communication circuit, confirm that both the indoor and outdoor units are receiving the correct power supply.
| Check | Action |
|---|---|
| Indoor unit | Check that 240 V AC is supplied to the indoor unit. |
| Outdoor unit / interconnection | Check the interconnecting supply and confirm that the outdoor unit is receiving the required 240 V AC supply. |
Important: Do not proceed with communication diagnosis until the required mains supply has been confirmed at both units.
2. Identify which unit has stopped communicating
Check the communication output from each unit. Depending on the model, the communication signal may appear as a stable DC voltage or as a varying/fluctuating DC voltage.
- Locate the indoor-to-outdoor terminal block.
- Confirm the interconnecting cable and terminal connections are secure.
- Measure the communication output in accordance with the applicable model's service information.
- Compare the indoor and outdoor communication outputs to determine which side is not transmitting.
- If communication is present at both units, investigate the interconnecting wiring for open circuit, short circuit, incorrect termination or high-resistance connections.
Model variation: Communication voltage is not identical across all product families. Some models use a relatively stable DC level while others show a fluctuating signal. Always compare the reading with the applicable service manual for the model being tested.
3. If the outdoor unit is not sending communication
Once the outdoor unit has been identified as the side not transmitting, check the outdoor power and inverter-control circuits before replacing the main PCB.
| 1 | Power supply PCB: Inspect the fuses and confirm that power is entering and leaving the power supply PCB correctly. |
| 2 | DC supply: If the power supply PCB is operating correctly, confirm that the DC supply for the system is present and within the value specified for the model. |
| 3 | Inverter components: Depending on the model, the DC circuit may include the diode bridge, IPM/TR PCB and/or ACTPM/Active Module. Test only in accordance with the applicable service manual. |
| 4 | Main PCB: Do not condemn the main PCB until its incoming power supplies and associated inverter-control components have been checked. |
4. Fan and compressor checks
If the communication circuit appears normal but the outdoor unit will not operate correctly, continue with component checks for the fan motor and compressor/inverter circuit.
- Check for obvious damage, loose plugs, burnt terminals or blown PCB fuses.
- Check the outdoor fan motor and associated drive circuit using the model-specific service procedure.
- Check compressor winding condition and insulation resistance where applicable.
- Check the inverter/IPM/TR PCB and active-filter/ACTPM circuits before condemning the compressor.
- Confirm that all plugs and connectors removed during testing are correctly refitted before restoring normal operation.
Diagnostic principle: First determine which unit has lost communication. Then prove the power supplies and component circuits on that side of the system. This prevents unnecessary replacement of the indoor or outdoor main PCB.
5. Legacy reference images
The original General Assist article included the following technical images. They are retained here as Freshdesk-hosted references and are not embedded as Base64 data.
Technical note: This is a legacy diagnostic reference. Exact communication voltages, terminal designations and inverter-component test values vary by model. Use the applicable service manual for final test values and component-specific procedures.