General Assist Technical Reference
DC Fan Motor (Two Plug Type) Testing
Diagnostic procedure for power, control and feedback circuits
Applicable to selected General and AIRSTAGE indoor units, including ARTG-series ducted models
Two-plug DC fan motors use a separate high-voltage power connector and low-voltage signal connector. Testing both circuits helps determine whether the fault is within the fan motor, indoor control PCB or connecting harness.
High-voltage hazard: The fan motor power circuit may carry approximately 310-340 V DC. Testing must only be completed by qualified service personnel using insulated probes and appropriate electrical safety procedures.
1. Identify the motor type
| Connector | Typical Construction | Purpose |
|---|---|---|
| Plug 1 - Power | Usually 3-core | High-voltage DC supply and reference connection |
| Plug 2 - Signal | Usually 5-core | Control command, feedback/tachometer and low-voltage reference |
ARTG65LHTA control PCB wiring diagram showing the fan motor connections.
2. Safety and preparation
| 1 | Isolate the indoor unit before disconnecting either fan motor plug. |
| 2 | Wait at least 5 minutes for the indoor PCB capacitors to discharge. |
| 3 | Use a digital multimeter rated for the expected DC voltage and fitted with insulated probes. |
| 4 | Confirm the wire colours and pin numbers against the model-specific wiring diagram before testing. |
3. Test the power plug
Reconnect the system, energise the unit and measure the DC voltage between the positive and negative fan motor supply terminals. Back-probe only where it can be completed safely without damaging the connector.
| Test | Typical Reading | Interpretation |
|---|---|---|
| V+ to V- | Approximately 310-340 V DC | High-voltage supply from the indoor PCB is present. |
| V+ to V- | 0 V DC | Check the indoor PCB power supply and fan drive circuit. |
| V+ to V- | Unstable or fluctuating | Possible PCB regulation, switching or supply issue. |
Voltage values are typical only. Confirm the correct value and pin arrangement from the applicable service manual before condemning a component.
4. Test the signal plug
| Typical Pin | Function | Typical Reading |
|---|---|---|
| 1 | 5 V reference | Approximately 4.8-5.2 V DC |
| 2 | Control / PWM input | Variable signal depending on commanded fan speed |
| 3 | FG feedback / tachometer | Pulsing signal while the fan is rotating |
| 4 | Signal ground | 0 V reference |
| 5 | Model-dependent / diagnostic | Refer to the unit wiring diagram |
Command different fan speeds and observe the control signal. A changing control signal confirms that the indoor PCB is attempting to regulate the motor. A feedback signal should also be present while the motor is rotating.
5. Fan motor resistance checks
Power must be isolated: Complete resistance tests only after both plugs are disconnected and the PCB has fully discharged.
| Resistance Test | Expected Result | Assessment |
|---|---|---|
| V+ to V- | Normally a high resistance that may change as internal capacitors charge | A very low stable resistance may indicate a shorted internal motor drive circuit. |
| Any terminal to frame earth | Open circuit / OL | Any continuity to earth requires further investigation and normally indicates motor replacement. |
6. Common fault patterns
| Symptom | Likely Area | Recommended Action |
|---|---|---|
| Breaker trips when the fan is connected or starts | Shorted fan motor or PCB drive circuit | Isolate, disconnect the motor and test the motor and supply separately. |
| Fan does not start, but high-voltage DC is present | Motor electronics, signal supply or control command | Check the 5 V reference, PWM/control signal, feedback circuit and harness. |
| Fan speed is erratic | PWM command, feedback signal or poor connection | Inspect the signal harness and connector pins, then verify command and feedback signals. |
| No 5 V reference at the motor | Indoor control PCB or harness | Check for a harness short before replacing the indoor PCB. |
7. Service verification
- Confirm normal operation at every available fan speed.
- Confirm that fan-related error codes have cleared.
- Inspect both connectors for heat damage, loose terminals, corrosion or discolouration.
- Secure all wiring away from the fan wheel and sharp sheet-metal edges.
- Record voltage and signal readings on the service report.
Diagnostic principle: High-voltage supply present + valid control signal + no motor operation generally points toward the fan motor. Missing high-voltage supply or control signals generally points toward the PCB, harness or upstream control logic.