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My dash blower motor died suddenly. After troubleshooting, I have full battery voltage at the 2 prong power plug to the motor, with the key on, but the motor doesn't run. It momentarily bumps every time the key is turned on. Hooking it to a battery directly makes it run at full speed. I have zero resistance from the plug ground to the frame. Knocking on the motor body does nothing.

Should I consider the motor bad?

 
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I'm thinking out loud here. According to the factory shop manual, if I get battery voltage at the 2 prong plug and the fan doesn't start, I'm supposed to replace the fan.

Hooking directly to a battery with over 200 amp capacity will make the fan run, but since the fuse on the car is only 40 amps, the resistor is lowering the amps required to run the motor. Since the motor doesn't run at 40 amps, it must be bad.

I ordered a new motor and will report the results.

 
Rep Power: 225

I would sooner suspect the blower resistor.

Hooking directly to the battery does not give it more "power". Here is a snip of the blower resistor troubleshooting from the service manual if you're interested.

 
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The factory manual says if there is battery voltage at the 2P connector, replace the blower motor. The other steps come before testing the 2P connector. There is full BV at the connector.
My resistor is 4 pin and isn't shaped like your picture. I did some tests on the resistor plug and it was good. However, I didn't do all the tests

 
Rep Power: 225

Yes I saw that as well. But the fan working when connecting directly to the battery indicates an issue with the fan wiring, not the fan. There is a diagnostic mode you could run to see if the HVAC has any faults.

 
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Thanks Brotato. I checked the resistor and the ohms test passed at 1.4 and then the second test showed a bad resistor. So, now the system is working thanks to your help.

I still don't understand how 12.6 V at the fan plug, supplied by the resistor would not start the motor. Yet 12.6 V from a battery would.

 
Rep Power: 225

What second test exactly? 1.4 ohms is technically outside of the range given in the troubleshooting step.

The resistor actually controls the ground side. Bad resistor would mean no ground. You would still have battery voltage on the other pin though.

 
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It WAS the resistor. I remember the ground side control topics from a course I took years ago. Thanks for the help

 
Rep Power: 225

I was right! Hopefully you can return the new blower motor.