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Last week the A/C fans on my 2004 Honda Accord LX failed. It wasn't quite all at once... the fans kicked in once or twice after the initial failure, but cut out again after a couple of minutes. After doing some research on the relevant bits (fuse under the hood, blower resistor, blower motor), I took a multimeter out to do some diagnosis.

The first measurement I made was to the pins of the power connector right at the blower motor. I unplugged it, turned the car accessory power on, turned the fan control on, and took a voltage measurement across the wires of the connector: 12V.

Is that sufficient to conclude that the issue is the blower motor itself? The only reason I hesitate is that most of the diagnosis articles/videos I've seen use a more purpose-built probe, such as this. I'm not sure if the resistor complicates the circuit in a way that might render a simple multimeter voltage reading at the motor insufficient. Is there anything else I should check before deeming the motor faulty?

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The blower has a resistor which varies the ground circuit. Which is how you get different fan speeds. You should have battery voltage at the blower motor connector. Your problem is most likely the blower motor. But you could also check the price of the resistor and maybe just change both.

  • Are there failure modes for the resistor that might still show 12V across the terminals at the blower motor, or can I take the 12V reading to mean that the resistor is ok? – glibdud Jul 9 '17 at 16:42
  • Usually when a resistor fails it will allow high speed. Most likely resistor is ok – cano Jul 9 '17 at 16:45

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