Q: Heater fan or resistors bad

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The heater fan comes on and shuts back off

My car has 300 miles.
My car has a manual transmission.

Hi There, It sounds like you may have a faulty blower motor relay. The resistor controls the fan speeds and the relay controls the power to the motor itself. Occasionally, the blower motor itself will wear out or become faulty working intermittently as the brush contacts inside the motor wear out. The blower motor relay supplies power to this motor when you turn the switch to "on" that can sometimes fail. When this happens, you may notice that you will not feel anything blowing out of the vents at all. This may also cause the blower motor to work intermittently as you describe. I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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