Overview
Field reports have identified intermittent cooling performance issues across Fujitsu Multi Systems — specifically AOTG36LBTA4 and AOTG30LBTA4 models — where some indoor heads fail to cool while others experience coil flooding.
This condition can often be misdiagnosed as a refrigerant charge issue or faulty electronic expansion valve (EEV) body, when in fact the underlying cause may be related to control PCB malfunction.
1. Reported Symptoms
Some indoor units not cooling at all, others overfeeding refrigerant (flooded coil).
System pressure readings inconsistent between heads.
Audible difference during EEV initialization — some valves faint or silent.
Refrigerant charge and EEV coil resistances test normal.
2. Preliminary Diagnostics
Initial fault-finding steps undertaken:
Refrigerant Reclaimed and full system charge verified — no improvement.
All four EEV bodies replaced — issue persisted.
Piping and wiring confirmed correct per schematic.
EEV electrical testing showed all four coils within factory resistance tolerance and continuity confirmed.
Despite correct mechanical and electrical readings, the issue remained unchanged — indicating a control logic or output fault.
3. Root Cause
Investigation revealed that the indoor EEV control outputs from the outdoor main PCB were inconsistent.
During system start-up:
Valve A produced the normal, strong initialization click.
Valves B, C, and D emitted faint or irregular sounds.
Electrical signal testing confirmed all four EEVs were being energized, but output voltage amplitude was significantly reduced on circuits B–D.
This pointed to a degraded control PCB driver circuit responsible for EEV actuation, causing improper metering and cooling distribution.
4. Corrective Action
Replaced outdoor control PCB (main board).
Recommissioned the system, verifying proper valve sequencing during initialization.
Confirmed all four EEVs produced a consistent, sharp activation sound at power-up.
System achieved uniform cooling performance across all indoor units.
5. Key Diagnostic Indicator
During system initialization, each EEV should emit an identical clicking or buzzing sound as the stepper motors calibrate.
| Observation | Indication |
|---|---|
| All EEVs sound consistent | Normal operation |
| One or more faint / silent | PCB signal fault or driver output issue |
| Random valve noise variation | Possible intermittent PCB or harness issue |
6. Field Advisory
When fault-finding multi-head systems:
Always listen to all EEVs during start-up before reclaiming charge or replacing components.
Uneven valve sounds indicate a control PCB output issue, not necessarily an EEV fault.
Save time and resources by performing this auditory test early in the diagnostic process.
7. Recommended Procedure Summary
| Check Point | Test / Observation | Expected Result |
|---|---|---|
| Refrigerant charge | Weigh in full charge | Verified |
| EEV coil resistance | Measure with multimeter | Within spec (typically ~500Ω) |
| Valve sound test | Power ON, listen for equal clicks | All consistent |
| Outdoor PCB output | Check for stable DC voltage to all EEVs | Uniform across channels |
| System operation | Cooling confirmed across all heads | Stable suction pressure, even coil temp |
Conclusion
Fault traced to outdoor main control PCB, where uneven EEV drive signal prevented correct refrigerant metering.
Replacing the PCB resolved the issue completely.
This serves as a valuable field diagnostic note — always verify EEV initialization sounds before proceeding with component replacement or refrigerant work.
AOTG30LBTA4 issues.
Some heads weren’t cooling at all and some were flooding the coil. Had suspected either faulty ev body or gas charge. Reclaimed full charge so ended up replacing all 4 body’s to only have the same issue still.
After checking out wiring/piping we noticed that not all ev’s sounded the same when initializing. Valve A sounded normal and B, C, D sounded faint. All 4 evs tested out correctly so we ended up replacing the control pcb which fixed our issue in the end. Something to keep in mind when fault finding these system is to make sure all valves make the same sound when initializing. It could save you a lot of trouble.