AOTG18LVCC - F100 Fuse Failure Due to Factory Wiring Error
This article summarises a factory quality investigation into repeated F100 fuse failures on AOTG18LVCC outdoor units from the same production lot. The investigation identified a factory wiring error that was not detected by the normal heat-run or sampling inspection processes.
Key finding: A wiring mistake was found in a production lot of 145 AOTG18LVCC units. The error could cause F100 fuse failure when compressor current increased, but could remain undetected during low-current factory testing.
Applies To
| Product | AOTG18LVCC |
| Affected production quantity | 145 units |
| Manufacture date | 19 July 2014 |
| Factory line | D line |
| Reported failure | Repeated F100 fuse failure |
Problem Detail
- Multiple F100 fuse failures were reported on AOTG18LVCC units.
- The affected units had been supplied from the same factory production lot.
- Stock units from that lot were inspected and a factory wiring mistake was identified.
Factory Analysis
1. Heat-Run Test
Factory heat-run records showed no abnormality. However, the normal heat-run process was not capable of reliably identifying this wiring error.
- Typical current during the heat-run test was approximately 3.7 A.
- At this current, the likelihood of F100 opening was considered very low.
- If compressor frequency remained low, F100 could remain intact even when the wiring mistake was present.
2. Patrol Inspection
Factory patrol inspection checked the wire colour, but did not check the wire thickness.
3. Sampling Inspection
- The visual inspection method was the same as the patrol inspection.
- An operational test was performed, but the test duration was short.
- Current during the test was approximately 2.1 A.
- The low current and short operating period meant the wiring mistake was not detected.
Why the fault escaped factory testing: The wiring error did not necessarily cause immediate failure. At low compressor frequency and low current, F100 could remain intact, allowing the unit to pass production testing.
Manufacturing Record
| Product | Line | Quantity | Date | Serial Range |
|---|---|---|---|---|
| AOTG18LVCC | D | 145 | 19 Jul 2014 | Not stated in source report |
Similar Products Checked
Similar models manufactured around the same period were checked. No equivalent wiring mistake was identified in the following lots:
| Product | Line | Quantity | Manufactured Date | Serial Number |
|---|---|---|---|---|
| AOTG22LVCC | B | 35 | 25 Jul 2014 | E004546 to E004580 |
| AOTG24LFCC | B | 55 | 25 Jul 2014 | E025389 to E025443 |
Root Cause
Cause of occurrence: Factory wiring error.
Cause of escape: The existing factory heat-run and inspection processes were not capable of reliably detecting this particular wiring mistake.
Cause of escape: The existing factory heat-run and inspection processes were not capable of reliably detecting this particular wiring mistake.
Factory Countermeasures
- The work instruction was revised to require checking wire thickness and the presence or absence of the sleeve.
- The patrol inspection check sheet was revised to include confirmation of lead-cable thickness.
- Factory leaders and workers were retrained using the revised documentation.
Product Action
| Product Status | Action |
|---|---|
| Already installed product | Take corrective action at the individual site if the problem occurs. |
| Stock product | No specific stock action was stated in the source report. |
| Manufactured product | Factory countermeasure already implemented. |
Service Guidance
- For AOTG18LVCC units with repeated F100 fuse failure, inspect the associated wiring carefully before replacing the fuse or PCB.
- Do not rely only on wire colour. Confirm the correct wire thickness and whether the required sleeve is fitted.
- A unit may operate normally at low compressor frequency even when the wiring error is present.
- If the unit belongs to the affected production period, treat the factory wiring configuration as a possible cause of repeated F100 failure.
- After correcting any wiring issue, complete normal electrical and operational checks before returning the system to service.