Overview

The DC Brushless Fan Motor operates using a high-voltage DC circuit (330–380V DC) and a 15V DC control circuit. It includes an integrated control board with feedback circuitry to communicate fan speed (RPM) to the main controller PCB.

This test verifies the electrical integrity of the motor and checks for mechanical obstruction or failure.

Safety Warning

⚠️ High Voltage Hazard
The fan motor contains high-voltage DC circuitry.
Do not disconnect or handle wiring while power is applied.

Testing Conditions

  • Ensure power is OFF and the circuit is fully discharged before testing.

  • Use a digital multimeter set to Diode Test Mode.

  • Visually inspect that the fan shaft spins freely without resistance.

Procedure

  1. Locate the Fan Motor Connector
    Identify the fan motor connector terminals:

    • Red: High Voltage DC (330–380V DC)

    • White: DC Control Power (15V DC)

    • Black: DC Ground

    • Yellow: Fan Speed Signal

    • Blue/Brown: Feedback Signal

  2. Electrical Test (Power Off – Diode Test)
    Measure resistance and voltage drop between the following terminals:

    RED LEADBLACK LEADEXPECTED VALUE
    Red → BlackO/L
    Red → White0.5V – 1.8V (varies by motor age)
    Black → Red0.8V – 1.1V
    Black → White0.4V – 0.6V

    Note: Older motors may show readings around 0.5V, while newer models may measure up to 1.8V.

  3. Mechanical Test

    • Manually rotate the fan blade.

    • Check for smooth, free rotation.

    • Any stiffness, grinding, or uneven movement indicates bearing or shaft seizure.

  4. Feedback Verification (if available)

    • Ensure the feedback signal wire (Blue or Brown) is connected correctly to the control PCB.

    • Faulty feedback may cause fan speed error codes or abnormal operation.

Diagnosis and Interpretation

ObservationDiagnosisAction
Readings match tableMotor circuit normalNo fault detected
Infinite resistance or 0V across all testsOpen or shorted motor circuitReplace motor
Shaft seized or restrictedMechanical faultReplace fan motor assembly
No RPM feedbackFeedback signal open or defective PCBReplace fan motor or controller PCB

Technical Notes

  • The fan’s internal PCB regulates rotation speed via PWM control and provides tachometer feedback to the indoor unit controller.

  • During operation, the fan receives 330–380V DC for power and 15V DC for control.

  • Disconnecting the motor while energized can damage both the motor and control PCB.