Summary
This training module gives technicians a concise, field-oriented understanding of PSAC standard inverter control. It covers system architecture, operating modes, airflow and frequency control, protective functions, and self-diagnostics mapped to commissioning and service tasks.
Learning objectives
By the end of this module, participants will be able to:
Explain how the indoor unit and outdoor inverter share control responsibilities.
Identify fan-speed profiles and compressor frequency ranges for cooling, heating, and dry modes.
Describe key protective behaviours (current limiting, freeze/overheat prevention, defrost).
Use built-in self-diagnosis to isolate faults quickly.
Applies to
Wall-mounted split systems with indoor induction-fan control and outdoor inverter-driven rotary compressor (PSAC family)
1) System architecture (who controls what)
Indoor unit (master logic): Receives user commands, runs indoor fan profiles, calculates targets, and issues operating commands (mode and frequency request) to the outdoor unit.
Outdoor unit (power stage): Drives compressor via inverter (variable frequency), runs outdoor fan and four-way valve, and returns status/alarms to the indoor controller.
Technician note: Treat the indoor PCB as the orchestration layer and the outdoor PCB as the actuator/power layer. When symptoms involve capacity tracking or mode transitions, check indoor sensors/logic first; when symptoms involve current, frequency, or drive faults, check the outdoor inverter stage.
2) Indoor fan control (profiles)
Auto and manual speeds; Quiet mode available. Typical speed points: Hi ~1330 rpm, Med ~1170 rpm, Lo ~990 rpm, Quiet ~800–850 rpm (mode-dependent).
Auto profiles modulate fan speed versus room/setpoint delta; rhythmic variation smooths airflow perception.
Field tip: For airflow complaints, confirm mode-specific RPMs and that Quiet has not been selected—current limits apply in Quiet.
3) Compressor frequency control (capacity)
Cooling: ~36–95 Hz operating range; ramps with room/setpoint delta and load. Upper limit depends on indoor airflow and outdoor temperature.
Heating: ~36–125 Hz operating range with higher permitted peaks; similar dependence on airflow and ambient.
Dry: Fixed/stepped control around ~58 Hz on start, then temperature-driven modulation within defined limits.
Technician note: If frequency caps “early,” check for antifreeze, high-pressure, or over-current protection engaging before suspecting a drive fault.
4) Louver/air-direction logic
Louvers default horizontal in cooling/dry and downward in heating; manual overrides are allowed with safeguards to prevent condensation issues.
5) Protective and supervisory functions
Current release (power limiting): Outdoor PCB reduces compressor frequency to stay within rated input current; thresholds differ for Quiet vs normal airflow.
Antifreezing (indoor coil): When indoor coil temperature drops near ~5–7 °C, frequency is reduced or compressor paused to prevent icing.
Discharge gas over-temperature: Frequency ramps down as discharge temperature approaches limit; hard stop at excessive values with auto-recovery after cooldown.
Cooling protections: High-pressure and intake-block detection.
Heating safeguards: High coil-temperature release, cool-draft prevention (fan hold-off), outdoor-fan-stop protection.
Defrost: Time- and temperature-based algorithm; typical defrost uses a fixed frequency with termination by outdoor coil temperature or elapsed time.
Commissioning check: If capacity appears capped, verify coil sensors, airflow settings, and outdoor air path before adjusting charge or replacing hardware.
6) Operating modes — what “good” looks like
Cooling: Starts at high frequency to pull down load, then trims; fan follows Auto curve unless manually fixed. Antifreeze may intervene near coil limits.
Heating: Allows higher peak frequency; warm-up fan control prevents cold blow; may enter defrost based on coil temperature and run-time integration.
Dry: Indoor fan ~800 rpm nominal with temperature-driven compressor control; de-icing logic protects the indoor coil.
Auto changeover: Selects cooling/heating/dry/monitor per room and outdoor temperature; includes monitoring hold behaviour and restart logic.
7) Service aids and usability features
Odour-prevention: Indoor fan stops/steps around compressor OFF/ON events to reduce discharge odours in cooling/dry.
Quiet mode: Lowers fan speed and applies a tighter current limit.
Manual Auto & Auto-restart: Body button can start Auto with defaults; system restarts with memorised settings after power return.
Timer logic: OFF/ON/Program/Sleep timers adjust setpoint trajectories before stop/start to reach comfort at the scheduled time.
8) Self-diagnosis (lamp codes)
Major classification shown by operation/timer lamp flash patterns; minor classification available via test button to refine the fault (serial signal, thermistors, indoor/outdoor PCB, fan lock/speed, refrigeration cycle).
Field workflow:
Read major code; toggle to minor for detail.
Correlate with operating state (cooling/heating/defrost).
Validate sensors and communication before replacing PCBs.
9) Commissioning checklist (quick use in the field)
Verify supply, polarity, and earth; run address/functional checks.
Confirm indoor fan RPMs per mode; ensure no unintended Quiet limit during capacity tests.
Observe commanded compressor frequency versus expected ranges for the mode and ambient.
Confirm outdoor airflow path; validate defrost entry/exit when applicable.
Record baseline coil/discharge temperatures and lamp-code status for future comparison.
10) Troubleshooting heuristics
Low capacity in cooling: Check indoor coil antifreeze intervention, airflow, and outdoor intake; rule out high-pressure protection.
Erratic heating: Validate cool-draft prevention and defrost logic; confirm sensor placement and health.
Frequent frequency clipping: Investigate current-limit triggers—dirty coils, blocked intake, or abnormal load—before suspecting inverter hardware.
Persistent alarms: Use lamp-code minor classification to target sensor vs PCB vs communication.