Outdoor Communication Error
Freshdesk Solution: Diagnostic flowchart and component test guide for outdoor communication error where likely causes include the main controller PCB, IPM / TR PCB, ACTPM / active filter module, DC fan motor and EEV coil.
Safety first. Isolate power before unplugging boards, fan motors, EEV coils or high-voltage harnesses. The training material states that IPM, diode bridge, ACTPM and EEV checks are performed with power off, and DC fan motors should not be disconnected while power is applied. Use appropriate lockout and discharge procedures before testing inverter components.
Quick fault logic
Confirm supply and wiring Confirm indoor to outdoor signal Check if a component is loading the PCB Isolate and test suspect parts Replace failed component and retest
Step 1 - Confirm communication before condemning power components
3-wire remote signal test
- At the wall controller, check Y1 to Y3 = 12V DC. If 12V DC is not present, the training guide notes the controller board could be faulty.
- Remove Y2 and test between Y3 and the disconnected cable to indoor: look for a fluctuating 7-11V DC pulse.
- Also test between controller terminals Y2 and Y3 for a fluctuating 7-12V DC signal.
Indoor to outdoor serial signal test
- Test between terminal 2 (neutral) and terminal 3 (signal) from both indoor and outdoor ends.
- If one end shows signal and the other does not, suspect damaged or disconnected signal cable between indoor and outdoor.
- If the communication circuit is missing with wiring confirmed, move the diagnosis toward the main controller PCB / signal chip.
| Signal reference | Expected value | Use |
|---|---|---|
| Remote Y1 to Y3 | 12V DC, not less than 11.4V | Confirms controller power to remote circuit |
| Remote Y2 to Y3 | 7-11V DC pulse | Confirms remote data signal |
| AST & ART/C indoor signal | 60-120V | Indoor communication reference |
| ASTA & ASTB indoor signal | 40-90V | Indoor communication reference |
| ASTG indoor signal | Approx. 200V static | Indoor communication reference |
| ARTG & 3 phase indoor signal | Approx. 295V static | Indoor communication reference |
| ARTH indoor signal | 50-250V | Indoor communication reference |
| AOTA outdoor signal | 60-120V | Outdoor communication reference |
| AOTG / AOTH outdoor signal | 3-110V | Outdoor communication reference |
Diagnostic principle: if the communication voltage is absent, start with wiring and the main controller PCB. If communication voltage is present but the fault persists, a connected outdoor component can still be pulling down the control circuit or causing the outdoor board to shut down intermittently.
Step 2 - How to check each suspect component
Main controller PCB
- Visually inspect for burn marks, damaged tracks, loose plugs, failed relay area or blown replaceable DC fuse 3.15A.
- Confirm the PCB has correct input supply and communication output present before disconnecting major components.
- Check the outdoor fan motor plug supply references on the board: red to black = 330-370V DC and white to black = 15V DC.
- Check the EEV output is a 12V DC circuit and the pressure sensor / thermistor circuits are 5V DC.
- If wiring and all connected components test correctly, but the signal remains missing or unstable, replace the main controller PCB.
IPM / TR PCB
Test method: power OFF, disconnect all control harnesses, multimeter on diode.
| Black lead | Red lead | Expected value |
|---|---|---|
| P | U | 0.4V |
| P | V | 0.4V |
| P | W | 0.4V |
| U | N | 0.4V |
| V | N | 0.4V |
| W | N | 0.4V |
| P | N | 0.7-0.9V |
| N | P | O/L |
A failed IPM can upset the outdoor controller and present as a communication-related shutdown. Any short, open or major deviation from the diode pattern is grounds to replace the IPM / TR PCB.
ACTPM / Active filter module
Test method: power OFF, disconnect all control harnesses, multimeter on auto-range resistance.
| Black lead | Red lead | Expected value |
|---|---|---|
| - | + | 360kΩ |
| - | L1 | 360kΩ |
| - | L2 | Over 1MΩ |
| - | N | 0Ω |
| + | P | 720kΩ to 900kΩ |
| N | P | 360kΩ to 540kΩ |
- Inspect the ACTPM for physical damage.
- The training guide states an ACTPM short will trip the power supply circuit breaker.
- If values are out of range or the breaker trip history points here, replace the ACTPM.
DC fan motor
Important: do not disconnect the DC fan motor when power is applied.
- Check mechanically whether the fan shaft is partially or fully seized.
- Test with power OFF using diode mode.
- Motor wiring reference: red = high voltage DC 330-380V, black = DC ground, white = 15V DC control, yellow = speed signal, blue/brown = feedback signal.
| Red lead | Black lead | Expected value |
|---|---|---|
| RED | BLACK | O/L |
| WHITE | BLACK | 0.5V to 1.8V |
| BLACK | RED | 0.8V to 1.1V |
| BLACK | WHITE | 0.4V to 0.6V |
If the motor is shorted, electrically abnormal or mechanically seized, replace the fan motor and inspect the board socket and harness for heat damage.
EEV coil
5-wire EEV coil
Test method: power OFF, resistance test.
- Test from red to white / orange / yellow / blue.
- Each should be 45Ω to 50Ω.
- Each wire to earth should read O/L.
6-wire EEV coil
Test method: power OFF, resistance test.
- Test red to white and red to orange = 45Ω to 50Ω.
- Test brown to yellow and brown to blue = 45Ω to 50Ω.
- All wires to earth should read O/L.
Physical checks for both EEV types
- Check for corrosion underneath where the EEV coil sits on the EEV body.
- Ensure the coil is clipped down and secured firmly to the EEV body.
- A shorted EEV coil or moisture-damaged coil can load the 12V DC output and create control issues that may appear as communication faults.
Step 3 - Decision guide
| Observed result | Likely direction | Action |
|---|---|---|
| No remote or indoor/outdoor signal voltage | Main controller PCB, signal chip, wiring fault | Repair wiring, confirm supply, replace controller PCB if signal cannot be restored |
| Signal present but fault remains | Connected outdoor component may be loading controller | Power off and isolate DC fan motor, EEV coil, IPM and ACTPM one by one |
| ACTPM out of range or breaker trip history | ACTPM failure | Replace ACTPM and inspect related harnesses |
| IPM diode readings incorrect | IPM / TR PCB failure | Replace IPM / TR PCB |
| DC fan motor electrically abnormal or seized | Fan motor failure | Replace motor and inspect board plug/socket |
| EEV coil resistance incorrect or short to earth | EEV coil failure | Replace EEV coil and confirm secure seating on valve body |
| All components test correctly | Main controller PCB remains primary suspect | Replace controller PCB and retest communication |
Final verification
- Reconnect all harnesses correctly.
- Restore power.
- Confirm indoor to outdoor communication signal is present.
- Clear the fault and perform a test run.
- Verify fan operation, EEV response, stable communication and normal system operation.