ARTC72LATU - Sirocco Fan Barrel Loose on Motor Shaft
This article summarises the quality assurance investigation into reports of the ARTC72LATU indoor fan barrel becoming loose on the motor shaft.
Issue Summary
- Product: ARTC72LATU
- Quantity referenced in the report: 16 units
- Reported issue: Sirocco fan barrel becoming loose on the motor shaft
- Likely symptom: Fan wobble and abnormal noise caused by the fan contacting the casing
Problem Description
Several ARTC72LATU units were reported with the fan barrel becoming loose on the motor shaft. Where the fan is not adequately secured, repeated operation may allow the retaining screw to loosen further, resulting in fan wobble and possible contact between the fan and casing.
Factory Investigation
1. Process Inspection History
The factory confirmed that there was no repair history recorded for the affected product.
2. Manufacturing Process Review
- Apply red screw-locking varnish near the hexagon socket.
- Insert the sirocco fan onto the motor shaft.
- Align the retaining screw with the D-cut section of the shaft.
- Tighten the screw using a manual torque wrench.
- Specified tightening torque range: 4.0 to 22.6 Nm.
- Confirm the mounting condition through cyclic inspection.
- Check for fan wobble.
- Minimum torque at which wobble was found to occur was approximately 0.5 to 1 Nm.
- During the noise inspection process, confirm noise, vibration and fan current at S-Low, Low, Medium and High fan speeds.
- Sampling inspection was also carried out using one unit from each lot to confirm operation, noise and abnormal sound.
3. Production Unit Check
Ten manufactured units were checked. Measured tightening torque was between 10 and 15 Nm.
4. Replication Testing
| Test | Result |
|---|---|
| Retaining screw tightened to 4 Nm, followed by 500 start/stop cycles | No screw loosening or abnormal noise found |
| Retaining screw tightened between approximately 1 and 3 Nm, followed by 500 start/stop cycles | No screw loosening or abnormal noise found during the replication test |
Factory assessment: If the tightening torque is below approximately 1 Nm, fan wobble may occur and this can lead to abnormal noise.
Likely Cause
- A small number of units may have left production with the retaining screw tightened too lightly.
- Repeated unit operation may then have allowed the screw to loosen further.
- The fan could then wobble and contact the casing, resulting in noise.
- Torque control was not sufficiently consistent because the assembly process relied on manual tightening.
- The replication test did not reproduce the fault, but the factory considered insufficient tightening to remain a credible cause.
Manufacturing Corrective Action
| Corrective Action | Implementation |
|---|---|
| Manufacturing process changed so the worker uses a torque wrench for the fan retaining screw | 18 July 2014 |
| Torque setting standardised to 20 Nm | 18 July 2014 |
| Additional tightening torque requirement added to the assembly specification | 2 September 2014 |
Action for Existing Product
- Already installed product: Inspect and rectify on a case-by-case basis if the fault occurs.
- Stock product: No blanket corrective action was specified in the original report, as the factory considered the issue unlikely to occur frequently.
- Current production: Manufacturing corrective actions had already been implemented.
Service Guidance
If an ARTC72LATU is reported with fan noise, fan wobble or suspected fan-to-casing contact:
- Isolate power and safely access the indoor fan assembly.
- Inspect the sirocco fan barrel for movement on the motor shaft.
- Check the retaining screw is correctly positioned on the D-cut section of the shaft.
- Inspect for evidence of the fan contacting the casing.
- Check the retaining screw condition and evidence of screw-locking compound.
- Where corrective tightening is required, follow the applicable service or manufacturing instruction for the model.
- After reassembly, operate the unit through all available fan speeds and confirm there is no abnormal noise, vibration or fan wobble.
Reference: Original quality assurance report referenced appendices covering inspection history, updated assembly specification and manufacturing process changes.