ARXA24GALH - EEV Not Opening Above 150 Steps / Forced Thermostat Off
This article summarises a factory quality investigation into an ARXA24GALH indoor unit where the electronic expansion valve (EEV) would not open above approximately 150 steps during commissioning. Replacing the indoor PCB resolved the fault.
Key finding: The unit was being held in forced thermostat off. Factory analysis found evidence that the PCB had previously been repaired in the area associated with CNA03 / CNA04, and the repair was considered inadequate.
Applies To
| Product | ARXA24GALH |
| Reported unit reference | R000148 |
| Reported symptom | EEV would not open above approximately 150 steps during commissioning |
| Field repair | Indoor PCB replaced - fault resolved |
Problem Detail
- During commissioning, the technician found that the EEV would not open beyond approximately 150 steps.
- The indoor PCB was replaced.
- After PCB replacement, normal operation was restored.
Service Tool Analysis
- The unit remained in thermostat off regardless of the selected operating mode, including test operation.
- The thermostat-off control itself appeared to operate normally.
- Because thermostat off remained active even during test operation, the factory suspected that forced thermostat off was being applied.
Relevant input: The factory report identifies CNA03 / CNA04 as the terminals associated with the forced thermostat-off input. A short or abnormal condition at this circuit can force the indoor unit into thermostat off.
PCB Inspection Findings
- The returned PCB showed signs that it had previously undergone repair work.
- The repaired area was associated with the CNA03 / CNA04 circuit.
- This supported the service-tool finding that the unit was being incorrectly held in forced thermostat off.
Factory Process Review
The factory confirmed that when a defective PCB was identified during production, repair staff could repair the board and return it to the production line.
At the time of this incident, repaired PCBs did not have a specific identification mark. As a result, it was not possible to confirm from the board alone whether it had previously been through the repair process.
Suspected Root Cause
Factory conclusion: The PCB repair work was suspected to have been inadequate. The report states that component/contact reliability may have deteriorated as PCB temperature changed during operation, causing the forced thermostat-off circuit to operate incorrectly.
Factory Countermeasures
- Provide additional training to factory personnel carrying out PCB repair work.
- Revise the PCB repair process.
- Add a circle mark (○) to the PCB when repair work has been carried out, so repaired boards can be identified.
Product Action
| Product Status | Action |
|---|---|
| Already installed product | Address on a case-by-case basis if the problem occurs. |
| Stock product | No action specified in the factory report. |
| Production product | Countermeasure already implemented. |
Service Guidance
- If an ARXA24GALH shows restricted EEV opening during commissioning, confirm whether the unit is actually being held in thermostat off.
- Use service data to confirm whether thermostat off remains active during test operation.
- Inspect the CNA03 / CNA04 forced thermostat-off circuit for a short, wiring issue, connector issue or PCB fault.
- If no external short or wiring cause is present, the indoor PCB should be considered as a possible cause.
- Replacement of the PCB resolved the reported case.