Overview
DC fan motors are self-contained, inverter-driven, variable-speed motors used across most indoor and outdoor units.
They are sealed units — meaning they cannot be repaired (e.g. bearings cannot be replaced).
These motors receive a speed signal from the main PCB based on compressor speed and ambient temperature, and return a feedback signal to the PCB for control logic.
dentification
DC fan motors are typically identified by a 5-pin multi-connector:
Red: DC High Voltage (330–380VDC)
Black: DC Ground
White: DC Control Power (15VDC)
Yellow: Fan Motor Speed Signal
Brown: Fan Motor Feedback Signal
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Testing and Safety Precautions
⚠️ Safety Warning:
Before disconnecting or reconnecting any DC fan motor, ensure the power is isolated and all DC voltage within the unit has discharged below 5VDC.
Never disconnect while energised.fan motor.1
Step-by-Step Testing Procedure
1. Verify DC Supply Voltages
Using a multimeter:
Between Black (Ground) and White (Control Power): expect ≈15VDC
Between Black (Ground) and Red (High Voltage): expect 330–380VDC
If voltage is missing or low, check the power PCB or wiring harness
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2. Check Connections
Inspect all leads and crimps in the multi-pin connector
Ensure the plug is securely fitted into the PCB
Look for any loose or backed-out terminals
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3. Mechanical and Diode Tests
Ensure the fan rotates freely — check for obstructions or debris.
Disconnect the motor before testing.
Using a digital multimeter in Diode mode, measure between the following pins on the motor plug:
| Positive Lead (RED) | Negative Lead (BLACK) | Expected Value |
|---|---|---|
| RED → BLACK | — | Open (OL) |
| BLACK → RED | — | 0.8–0.9 |
| WHITE → BLACK | — | 1.2–1.8 or OL |
| BLACK → WHITE | — | 0.4–0.6 |
Readings outside these values indicate internal motor failure
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4. Inspect for Mechanical Noise
On outdoor units, confirm the rubber boot/dust seal is seated correctly.
A misaligned seal may cause bearing or squeak noises that resemble motor failure
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Common Fault/Error Codes
| Code | Description |
|---|---|
| 51 | Indoor unit fan motor error (Fan 1) |
| 59 | Indoor unit fan motor 2 error |
| 97 | Outdoor unit fan motor error (Fan 1) |
| 98 | Outdoor unit fan motor 2 error |
| 11 | Serial communication error |
| 94 | Outdoor trip detection |
| A1/10.1 | Discharge temperature error |
| A5/10.5 | Low pressure error fan motor.1 |
Possible Causes of Motor Damage/Failure
Noisy or obstructed fan
Dirty or blocked coils/filters
Airflow restriction
Foreign material in fan barrel
Overheating from nearby equipment
Seized bearings or jammed fan
Loose or damaged fan blades
PCB or power supply failure
Unstable power input
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Recommended Action
Verify supply voltages and signals before replacing the motor.
Replace the entire fan motor assembly if found faulty — repairs are not possible due to its sealed construction.
Record all test readings and photos in the customer’s job notes for traceability.