Summary

This module distills the PMAL standard inverter control method for practical field use. It covers system architecture, serial signalling, compressor/fan/EEV control, defrost logic, protections, error confirmation, commissioning, and troubleshooting. No links.

Applies to

  • Wall-mounted split systems in the PMAL/related standard-inverter family

1) System architecture & wiring (what’s on each PCB)

  • Outdoor inverter PCB: discharge, outdoor-coil, and ambient thermistors; EEV; outdoor fan; 4-way valve; DIP switches.

  • Indoor PCB: room and indoor-coil thermistors; indoor fan; stepper louvre; DIP switches.

2) Serial signal between indoor and inverter (how they talk)

  • Two main frames exchange:

    • Indoor → Outdoor: operation mode, required capacity code, indoor pipe temperature, quiet-mode flag, model info.

    • Outdoor → Indoor: actual operation mode, outdoor temperature, defrost state, unit type, EEV initialise status, and outdoor protection status.
      Field tip: If capacity looks capped or the unit “idles,” read the required-capacity code and defrost bit first before suspecting hardware.

3) Compressor control (capacity ranges)

  • Typical frequency window 10–120 Hz with smooth ramp rates up and down.

  • Quiet mode reduces allowable frequency versus normal operation.

  • Cooling includes a lowest-revolution guard at high outdoor temperatures to protect the system.

4) Outdoor fan control

  • Two speeds (HI/LOW). Selection depends on outdoor temperature, mode/quiet status, and in cooling also on compressor frequency. Overrides apply at very high ambient and very low frequency.

5) EEV control (initial pulses and tracking)

  • At start, the valve opens to an initial pulse based on outdoor temperature and mode.

  • During operation, the EEV tracks a target discharge-temperature map that depends on outdoor temperature and compressor frequency.

  • Heating exception: very low indoor-coil temperature forces outdoor fan to HI to push heat through the coil.

6) Defrost sequence (heating)

  • Start condition: accumulated heating run time plus sufficiently low outdoor-coil temperature.

  • Sequence: compressor/fan stop → EEV to a larger opening → 4-way valve changeover → controlled timings → compressor restart.

  • Finish condition: elapsed time or outdoor-coil temperature recovery, then normal heating resumes.

7) Protections (what limits capacity or trips)

  • Discharge temperature: staged frequency reductions; stop at excessive temperature; auto-recovery after cooldown.

  • Current limit (DIP-selectable): compressor frequency trimmed so outdoor input current does not exceed the configured limit.

  • Heating overload / indoor-coil high temp: graded reductions, then stop if necessary.

  • Low-ambient cooling / outdoor-coil high temp: staged reductions with hard stop if limits are exceeded.

8) Error confirmation (LED meanings for fast triage)

  • Outdoor inverter PCB LEDs: patterns identify serial communication error, thermistor faults, IPM/overcurrent, current transformer error, active filter module fault, compressor location error, high-pressure, and outdoor-fan error.

  • Indoor unit LEDs: indicate room/coil thermistor issues, indoor-fan error, and mirrored outdoor errors.

  • Use the “times OFF/ON” count method to distinguish first vs. repeated occurrences and to identify permanent-stop cases.

9) Commissioning checklist (field-ready)

  1. Wiring & DIP: Verify terminations, EEV and fan connectors, and DIP selections (including current-limit DIP).

  2. Sensors: Confirm room/coil/ambient/discharge thermistors read sensibly at ambient.

  3. Run-up test: Observe required-capacity code and resulting frequency; verify quiet-mode behaviour and lowest-revolution guard in cooling.

  4. Fan & EEV: Check outdoor-fan HI/LOW transitions vs ambient and frequency; confirm initial EEV pulses and stable tracking.

  5. Heating test: Observe cold-draft prevention, then verify defrost eligibility and clean exit.

  6. Protections: Briefly constrain airflow to confirm current-limit/temperature protections respond (restore normal airflow immediately).

  7. Record: Log ambient, coil/discharge temps, compressor Hz, and LED status for your baseline.

10) Troubleshooting heuristics

  • Early frequency clipping: usually current-limit or temperature protection—check DIP setting, airflow, coil cleanliness, and ambient.

  • Hunting/poor capacity: verify indoor-pipe temperature in the serial data; re-seat EEV connector and confirm discharge sensor contact.

  • Stops in heat at low ambient: check defrost entry criteria, outdoor-coil sensing, EEV pulses, and 4-way valve operation.

  • Outdoor fan-related trips: match LED code to fan or active-filter faults; test under controlled conditions.

Key takeaways

  • The platform relies on serial capacity codes, mapped frequency tables, and target-discharge-temperature EEV control; protections trim capacity before tripping.

  • Fast diagnosis comes from reading serial fields, watching frequency vs expected tables, and decoding LED patterns precisely.