AOTH36KBTA5 - Noisy Compressor Flow Chart
Troubleshooting flow for abnormal outdoor unit compressor noise, based on field findings and successful rectification using the upgraded inverter PCB software.
Model covered: AOTH36KBTA5
1. Main troubleshooting flow
| Start: Customer reports abnormal outdoor unit noise Customer may advise there are no consistent conditions or patterns to when the noise occurs. |
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| Step 1 - Access and prepare outdoor unit Access outdoor unit, dismantle as required, attach gauges and connect the service tool. |
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| Step 2 - Reproduce the operating condition Run all indoor units in heating at 30°C to drive the system and simulate the noise complaint. |
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| Step 3 - Monitor compressor operation Use the service tool to watch compressor speed while observing the outdoor unit. |
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| Decision - Can the noise be heard during compressor speed change? In the known case, noise occurred as the compressor changed from low speed to high speed and when ramping down significantly. |
| Yes - Noise reproduced | No - Noise not reproduced |
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| Proceed with component observation. Remove the compressor blanket if required and visually observe compressor movement while the speed changes. Known field symptom: Compressor was jolting up and down and creating a significant clunking noise. | Unable to confirm on site. Ask customer for conditions when noise is most common, record ambient/load conditions, and if possible request a video recording. Re-test during high load heating operation and monitor compressor speed transitions. |
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| Decision - Is the noise clearly coming from the compressor during speed transition? |
| Yes | No |
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| Suspect compressor driving issue. If compressor movement/noise aligns with changing speeds, suspect inverter PCB / software strategy rather than a random cabinet noise. | Investigate other noise sources. Check fan assembly, pipe vibration, cabinet panels, compressor mounts, valves and refrigerant line contact points. |
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| Temporary conclusion If noise is traced to compressor speed transition and compressor jolting is observed, suspect inverter PCB and software revision. |
2. Key findings from site diagnosis
| Check item | Observed result | Interpretation |
|---|---|---|
| Heating test at 30°C with all indoors running | Noise successfully reproduced under load | Confirms fault is operational rather than cosmetic |
| Service tool compressor monitoring | Noise occurred as compressor changed speeds, especially low to high and on ramp-down | Points to compressor driving/control strategy |
| Visual inspection with compressor blanket removed | Compressor jolting up and down with significant clunking | Supports inverter PCB / software related noise issue |
3. Rectification flow
| Start rectification: Return to site and isolate power |
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| Step 1 - Dismantle outdoor unit and disconnect old inverter PCB Remove the existing PCB with the old software revision. |
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| Step 2 - Install upgraded software PCB Supply and install the updated inverter PCB/software version. |
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| Key software change Updated software changes the minimum compressor speed from 10 rps to 18 rps to eliminate the noise issue. |
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| Step 3 - Test operation after repair Run the system and confirm lowest compressor speed now holds at 18 rps and the abnormal noise is no longer present. |
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| End result No noise present. Advise customer to monitor and report if any further issues arise. |
4. Practical technician guidance
What to check on site
- Whether the noise can be reproduced under load.
- Compressor speed behaviour on the service tool.
- Whether the noise occurs during ramp-up or ramp-down transitions.
- Whether the compressor itself is physically jolting or clunking.
- Whether the noise appears linked to inverter control rather than fan/cabinet vibration.
What this known fix indicates
- This issue has been successfully resolved by replacing the inverter PCB with the upgraded software version.
- The updated software raises the minimum compressor speed from 10 rps to 18 rps.
- If the same symptom is present, this known fix should be considered early in diagnosis.
Note: If the noise is not coming from the compressor, do not assume the PCB is the cause. Rule out fan noise, loose panels, pipe vibration and other mechanical causes first.
5. Suggested ticket note
Suggested wording:
Customer reported abnormal outdoor unit noise. Outdoor unit accessed and dismantled. Gauges attached and service tool connected. All indoor units test run on heating at 30°C to reproduce complaint. Compressor operation monitored via service tool. Noise confirmed during compressor speed transition, particularly as compressor changed from low speed to high speed and during ramp-down. Compressor blanket removed and compressor observed jolting up and down with significant clunking. Noise confirmed as coming from compressor. Suspected compressor driving issue / inverter PCB software issue. On return visit, system isolated and old inverter PCB removed. Upgraded software PCB installed. New software changes minimum compressor speed from 10 rps to 18 rps. System tested, lowest compressor speed confirmed at 18 rps and abnormal noise no longer present. Customer advised to monitor operation and report any further issues.
Customer reported abnormal outdoor unit noise. Outdoor unit accessed and dismantled. Gauges attached and service tool connected. All indoor units test run on heating at 30°C to reproduce complaint. Compressor operation monitored via service tool. Noise confirmed during compressor speed transition, particularly as compressor changed from low speed to high speed and during ramp-down. Compressor blanket removed and compressor observed jolting up and down with significant clunking. Noise confirmed as coming from compressor. Suspected compressor driving issue / inverter PCB software issue. On return visit, system isolated and old inverter PCB removed. Upgraded software PCB installed. New software changes minimum compressor speed from 10 rps to 18 rps. System tested, lowest compressor speed confirmed at 18 rps and abnormal noise no longer present. Customer advised to monitor operation and report any further issues.