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Old 05-29-2015, 04:30 PM   #1
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Central AC fan problem


Last year before we stopped using the central air the motor would shut down by itself. I would turn the fan with a screwdriver and it would start right up. It also sounded like the bearing was going.

This spring I uncovered the ac and installed a new motor. Turned everything on and it worked fine and the house cooled right down. The first day it ran all day with out any problems. The second day after running about 5 hours the fan shut down and I could hear the condenser humming and the unit was getting hot, so I shut it down. I let it cool down and put it back into service and it ran fine until I shut it down for the night. Today same thing, ran fine most of the day, fan stopped after 4 or 5 hours and I shut it down. This time I cleaned the fins with the hose and ran a mist over the fan. It started right up.

Any ideas.

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Old 05-29-2015, 04:49 PM   #2
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Did you also replace the fan motor run capacitor when switching out the motor?

How much dirt came out of the fins?

Is the air blowing out the top of the unit with good force?

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Last edited by zappa; 05-29-2015 at 04:52 PM.
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Old 05-29-2015, 05:22 PM   #3
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Quote:
Originally Posted by zappa View Post
Did you also replace the fan motor run capacitor when switching out the motor?

How much dirt came out of the fins?

Is the air blowing out the top of the unit with good force?


Did not replace the run capacitor.

Not much dirt came out because I wash it out 2 times a summer.

Air is coming out in good force.

Went outside to check the motor. It has the same specs as the old motor. Took the cover off and the fan was very hot. After I put the top back on the fan didn't start up.

Just put the breaker back on after 15 minutes and it started right up.
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Old 05-29-2015, 05:23 PM   #4
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Was the motor an exact changeout? How about the capacitor? Was the capacitor bad on the old motor? What's the voltage and amp draw on the new motor?

Edit-just saw the post. Check the capacitor. There's a high chance your old motor was fine and just the cap was bad.
Always change the capacitor when changing a motor!
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Old 05-29-2015, 05:41 PM   #5
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Quote:
Originally Posted by roughneck View Post
Was the motor an exact changeout? How about the capacitor? Was the capacitor bad on the old motor? What's the voltage and amp draw on the new motor?

Edit-just saw the post. Check the capacitor. There's a high chance your old motor was fine and just the cap was bad.
Always change the capacitor when changing a motor!
The capacitor will make the fan run hot? Also I read if the fan isn't positioned correctly in the unit it won't draw enough air to cool the motor too.
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Old 05-29-2015, 05:41 PM   #6
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Quote:
Originally Posted by roughneck View Post
Was the motor an exact changeout? How about the capacitor? Was the capacitor bad on the old motor? What's the voltage and amp draw on the new motor?

Edit-just saw the post. Check the capacitor. There's a high chance your old motor was fine and just the cap was bad.
Always change the capacitor when changing a motor!
Agreed...the "bearing noise" may have been a failing capacitor.
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Old 05-29-2015, 05:47 PM   #7
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Quote:
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Agreed...the "bearing noise" may have been a failing capacitor.

So a bad capacitor can cause an overheating of the motor?
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Old 05-29-2015, 05:54 PM   #8
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So a bad capacitor can cause an overheating of the motor?
Yes, both if it looses capacitance or starts shorting out internally which causes the winding to draw too much current.
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Old 05-29-2015, 05:55 PM   #9
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Yes, both if it looses capacitance or starts shorting out internally which causes the winding to draw too much current.
Will replace the capacitor on Monday. Will let you know the outcome. Thanks.


Just pulled out the capacitor, not bulged out like I have read bad ones are, but rusty on the terminals.

Last edited by stevez; 05-29-2015 at 06:00 PM.
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Old 05-29-2015, 06:28 PM   #10
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Do you have a meter with a capacitance function?
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Old 05-29-2015, 08:00 PM   #11
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Quote:
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Do you have a meter with a capacitance function?
I have a fluke meter, I would have to check. How would you check a capacitor.
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Old 05-29-2015, 09:13 PM   #12
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With a meter that reads capacitance
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Old 05-29-2015, 09:52 PM   #13
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Quote:
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With a meter that reads capacitance

I know that, what do you measure across the leads.
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Old 05-29-2015, 10:05 PM   #14
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Disconnect the wires and measure across the terminals. If it's a dual cap then measure the C terminal to either the HERM terminal (compressor) or FAN terminal.
Use care as the capacitor can store voltage and give you a really good bite if you handle it wrong.

Last edited by roughneck; 05-29-2015 at 10:07 PM.
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Old 05-29-2015, 10:39 PM   #15
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A bad motor can damage a capacitor, and vice versa. I always try to change both, or at least test the capacitance.

I ALWAYS check the current draw of the motor and make sure it's under tolerance of the new motor. Blade positioning will make a difference here. (use an amp clamp on the common wire for the fan)

Double check the temp rating also. While everything looks similar, it could have a different temp rating. A rating below the environment will also cause your symptoms. (40C is minimum, while we like to use 70C rated Motors for condensers)

Most recent small motors that I've received have bolts that are over torqued. (Mexican manufacturers are the worse for this atm.) My supplier sometimes will loosen the bolts, right in front of me until the shaft spins freely. (after he complained of it, I always check now)

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