General Assist Technical Reference
PMAL Standard Inverter Control
Field guide to control logic, protections, commissioning and troubleshooting
For wall-mounted split systems in the PMAL and related standard-inverter family
This guide summarises the PMAL standard inverter control method for practical field diagnosis. It covers system architecture, indoor/outdoor serial signalling, compressor and fan control, EEV behaviour, defrost logic, protection functions, LED fault confirmation, commissioning and troubleshooting.
1. System architecture and wiring
| PCB | Main connected devices |
|---|---|
| Outdoor inverter PCB | Discharge thermistor, outdoor-coil thermistor, outdoor ambient thermistor, EEV, outdoor fan, 4-way valve and DIP switches. |
| Indoor PCB | Room thermistor, indoor-coil thermistor, indoor fan, stepper louvre and DIP switches. |
2. Indoor / outdoor serial signal
The indoor and outdoor PCBs exchange two primary data frames:
| Direction | Typical information |
|---|---|
| Indoor → Outdoor | Operation mode, required capacity code, indoor pipe temperature, quiet-mode flag and model information. |
| Outdoor → Indoor | Actual operation mode, outdoor temperature, defrost state, unit type, EEV initialise status and outdoor protection status. |
Field tip: If capacity appears capped or the system appears to idle, check the required-capacity code and defrost status before assuming a hardware fault.
3. Main operating controls
Compressor control
- Typical compressor frequency range is 10-120 Hz, with controlled ramp-up and ramp-down.
- Quiet mode lowers the allowable compressor frequency compared with normal operation.
- In cooling, a lowest-revolution guard applies at high outdoor temperature to protect the system.
Outdoor fan control
The outdoor fan uses HI / LOW speed control. Selection depends on outdoor temperature, operating mode, quiet-mode status and, in cooling, compressor frequency. Overrides can apply at very high ambient temperature and very low compressor frequency.
EEV control
- At start-up, the EEV moves to an initial pulse position based on outdoor temperature and operating mode.
- During operation, the EEV tracks a target discharge-temperature map based on outdoor temperature and compressor frequency.
- In heating, very low indoor-coil temperature can force the outdoor fan to HI to increase heat transfer.
4. Defrost sequence - heating
- Start condition: Accumulated heating run time plus sufficiently low outdoor-coil temperature.
- Sequence: Compressor/fan stop → EEV moves to a larger opening → 4-way valve changes over → controlled timing sequence → compressor restarts.
- Finish condition: Defrost ends by elapsed time or outdoor-coil temperature recovery, after which normal heating resumes.
5. Protection functions
| Protection | Typical response |
|---|---|
| Discharge temperature | Staged compressor-frequency reductions, stop at excessive temperature and automatic recovery after cooldown. |
| Current limit | DIP-selectable limit. Compressor frequency is reduced so outdoor input current remains within the configured threshold. |
| Heating overload / high indoor-coil temperature | Progressive frequency reduction, followed by stop if required. |
| Low-ambient cooling / high outdoor-coil temperature | Staged reduction and hard stop if protection limits are exceeded. |
Important: Many protection functions reduce capacity before a hard trip occurs. A system running below expected output is not automatically defective - confirm whether a protection is active first.
6. Error confirmation and LED triage
- Outdoor inverter PCB LEDs: Can indicate serial communication faults, thermistor faults, IPM/overcurrent, current transformer faults, active filter module faults, compressor location error, high-pressure faults and outdoor-fan faults.
- Indoor unit LEDs: Can indicate room/coil thermistor faults, indoor-fan faults and mirrored outdoor-unit faults.
- Use the specified times OFF / ON count method to distinguish first and repeated fault occurrences and to identify permanent-stop conditions.
7. Commissioning checklist
- Wiring and DIP: Verify terminations, EEV and fan connectors, and DIP selections including current-limit settings.
- Sensors: Confirm room, coil, ambient and discharge thermistors read plausibly at ambient conditions.
- Run-up test: Observe required-capacity code and resulting compressor frequency. Confirm quiet-mode behaviour and cooling lowest-revolution guard.
- Fan and EEV: Check outdoor-fan HI/LOW transitions against ambient and compressor frequency. Confirm initial EEV movement and stable control.
- Heating test: Confirm cold-draft prevention, then verify defrost eligibility and a clean return to heating.
- Protections: If testing protection behaviour, use controlled conditions and immediately restore normal airflow after the check.
- Record: Log ambient temperature, coil and discharge temperatures, compressor frequency and LED status as a baseline.
Safety: Do not deliberately create unsafe operating conditions. Any controlled airflow restriction or live diagnostic test must be brief, supervised and performed by qualified personnel with the system restored to normal immediately afterwards.
8. Troubleshooting heuristics
| Symptom | What to check |
|---|---|
| Compressor frequency clips early | Current-limit setting, protection status, airflow, coil cleanliness and ambient conditions. |
| Hunting or poor capacity | Indoor-pipe temperature in serial data, EEV connector seating and discharge thermistor contact. |
| Stops in heating at low ambient | Defrost entry criteria, outdoor-coil sensing, EEV operation and 4-way valve operation. |
| Outdoor fan-related trip | Match the LED code to outdoor-fan or active-filter faults and test under controlled conditions. |
9. Key takeaways
- The platform relies on serial capacity codes, mapped compressor-frequency tables and target-discharge-temperature EEV control.
- Protection logic typically trims capacity before a trip occurs.
- Fast diagnosis comes from checking serial fields, comparing actual frequency against expected control behaviour, and decoding LED patterns correctly.
General Assist technical reference. Always follow model-specific service documentation where values or sequences differ.