DC Fan Motor Supply and Control Test (Power ON)

Quick Answer

  • Red to Black: 330–380 V DC

  • White to Black: 15 V DC

  • Key rule: Do not disconnect fan plugs with power applied.

What is it?

A confirmation that the fan has correct HV DC supply and 15 V control supply from the PCB.

Tools

  • DMM (DC voltage)

Procedure

  1. With power ON, measure at the fan motor connector:

    • Red → Black

    • White → Black

Pass Criteria

  • 330–380 V DC (Red–Black)

  • 15 V DC (White–Black)

If it fails (Solution)

  • No/low HV DC:
    Action: Diagnose DC bus and power electronics (rectifier/ACTPM/IPM path).

  • No 15 V DC:
    Action: Suspect PCB low-voltage supply fault or a short on the 15 V rail; isolate loads and reconnect one-by-one.

  • Rails OK but fan not running:
    Action: Perform “DC Fan Motor Diode Test (Power OFF)” and check for seized shaft.

DC Fan Motor Diode Test (Power OFF)

Quick Answer (diode mode)

  • Red → Black: O/L

  • Red → White: 0.5–1.8 V

  • Black → Red: 0.8–1.1 V

  • Black → White: 0.4–0.6 V

What is it?

A diode-mode test to confirm internal fan driver circuitry is not shorted/open.

Tools

  • DMM (diode mode)

Procedure

  1. Isolate power.

  2. Disconnect fan motor harness.

  3. Perform diode tests using the combinations above.

Pass Criteria

  • Readings fall within the stated ranges.

If it fails (Solution)

  • Shorts or O/L where conduction expected:
    Action: Replace fan motor assembly.

  • Passes but still fails in operation:
    Action: Re-check HV DC and 15 V control supply; check mechanical seizure.