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Old 10-21-2008, 09:39 AM   #1
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Bad motor or capacitor going bad


I have a 12 year old Lennox furnace but the blower motor was replace 3 years ago. When I run the motor on manual I have the usual start hum and everything sounds fine. When I run it with the AC it seems to hum for a bit and then sounds OK, then will hum again. When I run it with heat it is ungodly loud. Is this simply the motor going belly up already or could a run capacitor that is weak cause a motor to run poorly on low speeds?

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Old 10-21-2008, 12:13 PM   #2
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Bad motor or capacitor going bad


As I recall capacitors decay exponentially, so if you back-probe your capacitor for voltage, power the fan on and off and it does not decay properly then it may be the problem.

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Old 10-21-2008, 10:37 PM   #3
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Bad motor or capacitor going bad


And curse up a storm when you get hit with close to 370 volts from the cap.
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Old 10-21-2008, 11:12 PM   #4
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Bad motor or capacitor going bad


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And curse up a storm when you get hit with close to 370 volts from the cap.
If it's just starting the inrush current will blast his "O"ring thru the seat of his pants!
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Old 10-21-2008, 11:15 PM   #5
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Bad motor or capacitor going bad


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As I recall capacitors decay exponentially, so if you back-probe your capacitor for voltage, power the fan on and off and it does not decay properly then it may be the problem.

I repectfully submit to you that you change the meter setting to capacitance and read the cap's Micro farad value.
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Old 10-22-2008, 08:01 AM   #6
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Bad motor or capacitor going bad


Yes, please disregard. Its probably not worth your time to test it.
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Old 10-22-2008, 09:31 AM   #7
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Bad motor or capacitor going bad


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Yes, please disregard. Its probably not worth your time to test it.
Oh,it's very well worth the time to check it, but safely.

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