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Old 09-14-2020, 06:10 PM   #1
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Indoor fan motor question


The AC unit suddenly stopped working. The AC tech who came over told me the indoor fan motor - set to medium speed wasn't running. So, he changed the speed to high and the fan started up again.

I asked why the indoor motor fan runs on high but not medium speed.

The AC tech said he didn't know... these things just happen.

I'm glad the AC is running but I am concerned something might still be wrong. Perhaps the AC tech missed something.

Any thoughts on this?

Last edited by ken33xx; 09-14-2020 at 06:31 PM.
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Old 09-14-2020, 07:02 PM   #2
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Re: Indoor fan motor question


A weak run capacitor can cause the motor to not have power to start moving on the lower speeds.

Did your tech check the capacitor?

The motor usually has 3-5 speed taps and it's possible a broken wire/connection inside the motor to affect the lower speeds. The solution in this case is to replace the motor, not increase the speed as doing so negatively impacts dehumidification.

Both problems can easily be identified with a multi-meter - the former requires a meter that read capacitance, many cheap ones don't.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 09-14-2020, 08:39 PM   #3
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Re: Indoor fan motor question


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Originally Posted by user_12345a View Post
A weak run capacitor can cause the motor to not have power to start moving on the lower speeds.

Did your tech check the capacitor?

The motor usually has 3-5 speed taps and it's possible a broken wire/connection inside the motor to affect the lower speeds. The solution in this case is to replace the motor, not increase the speed as doing so negatively impacts dehumidification.

Both problems can easily be identified with a multi-meter - the former requires a meter that read capacitance, many cheap ones don't.

O.k. here's what I asked and he's the AC tech response:

Me: I have a question: a weak run capacitor can cause the motor to not have power to start moving on the lower speeds. But if I understand correct the run capacitor is working fine. Is it possible a faulty wire or connection inside the motor affected the lower speeds?

AC tech: Absolutely if it seems like the motor might start to go let us know ASAP I got the model on serial number logged in an email from my guy and we'll get a warranty motor if needed.


The AC unit is 3 years old so the parts are under warranty. Still, I would feel better if he simply changed the motor today.

I'm in AZ and we have extreme heat 4 months of the year.
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Old 09-14-2020, 08:46 PM   #4
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Re: Indoor fan motor question


The motor may not be bad - the cap needs to be tested if it hasn't.

If that tap is bad, yes the motor should be replaced.
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Old 09-14-2020, 09:45 PM   #5
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Re: Indoor fan motor question


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Originally Posted by user_12345a View Post
The motor may not be bad - the cap needs to be tested if it hasn't.

If that tap is bad, yes the motor should be replaced.
Ok. thank you!!
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Old 09-15-2020, 06:55 PM   #6
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Re: Indoor fan motor question


Running the motor at a higher speed than that recommended for your system capacity is a kludge, not a fix. If the capacitor doesn't fix it they need to replace the motor.
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Old 09-16-2020, 10:50 AM   #7
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Re: Indoor fan motor question


If it's a Genteq it may have a 10 year warranty.
Labor not covered so you'll pay for that.
Pull motor, replace with same part # but may require programming.
Also, change your filter regularly as these fans are sensitive to pressure change beyond design. Ask for a free static pressure measurement while tech is there.
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