Have I done the correct thing?

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Old 08-17-13, 12:05 PM
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Question Have I done the correct thing?

My outside compressor (Lennox system) fan started humming and wouldn't start this morning. I tested the fan by pushing it with a pencil, and it would start.

I opened up the access panel, and saw that I had 2 separate caps, 1 single cap for the fan, 1 dual cap running the compressor. The fan cap was bulging, so I didn't even bother to test it figuring it was bad.

Upon further inspection, the compressor cap was actually a dual cap, and the fan side of that cap had the same rating as the bad single cap I pulled out.

Sooo, since the parts houses are closed today, I just hooked up one of the fan leads to the common post (it now has both compressor and fan lead on it now), and the other fan lead to the fan post. The fan now starts up and is working fine. I cycled the system a couple of more times to be sure.

My concern is if I have done something wrong or unsafe here. The compressor was installed 8 years ago by a local Lennox dealer, and that's the way it was originally installed. The single cap was tie wrapped to the mounting bracket of the dual cap, so considering that the dual cap was actually mounted by the MFG, I assumed there was a reason for this.

Is it OK to have the 2 separate connections to the cap common post? Would it be even necessary to rewire the contactor? Again, the system is running fine now.
 
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Old 08-17-13, 03:04 PM
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If the dual capacitor had an "unused" section that's the right capacitance, there shouldn't be a problem doing what you did. I assume that the common terminal on the dual capacitor is electrically connected to the same point that the original fan capacitor was. If not, then there may be a problem.
 
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Old 08-17-13, 03:34 PM
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The dual's unused (fan) capacitance was the same (7.5MFD @ 440VAC) as the old cap. Electrically (polarity?) I don't have any way of knowing, since a single is not marked. Is there a difference considering it's a capacitor?
 
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Old 08-17-13, 03:42 PM
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The capacitors used in A/C units are non-polarized, so polarity is not an issue. As long as as it's wired correctly (which I suspect it is), there shouldn't be a problem.
 
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Old 08-17-13, 05:04 PM
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THX. Still working strong and no smoke! It's mid '90's here today, and the compressor has been kicking on and off all day.
 
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Old 08-18-13, 04:44 AM
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A run capacitor is designed to continuously bleed a small amount of current to an extra winding to make the motor more efficient.
What you have done by connecting it to the common terminal is instead of bleeding a small amount of current is to give the extra winding the full amount of current it can draw which will cause the motor to overheat.

Not necessarily the current draw of your motor but an example is that the current draw on the capacitor connected motor leg could be 1/2 amp where as the direct connected current draw could be 2 amps.
Not a huge current draw but more than the motor is designed for.

Stop the unit after a few hours of running and see how hot the motor is.
 
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Old 08-18-13, 06:47 AM
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Thanks GregH, this is exactly the kind of response I was hopeful to get. I did notice yesterday that the panel above the motor felt a little warm. But then again, the sun was beating down on the unit. I ran the system 2 hours this morning, and the panel doesn't feel so warm.

I do have a second smaller zone in the house I don't normally run, but I'll run them both side by side to see if there's any huge difference.

Of note, the smaller compressor has the dual cap. The common post has a single purple wire, not two separate wires for the different motors. I figure the wiring is split up further down the line near or at the contactor.

So what I'm getting at here is that I think you're telling me I might be running the fan (on the broken unit) on a run capacitor, not a start capacitor. Or that I might be doubling the current going to the motor by virtue of sharing the common post. Is this correct? If so, I have no issue going to the supply store tomorrow to pick up a replacement cap. I certainly don't want to fry the fan motor.
 
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Old 08-18-13, 08:10 AM
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A start capacitor is not always but often made of black plastic and is in a range that is higher than about 90 mfd and is always connected to a motor or compressor start winding through some type of relay.
A run capacitor is normally in a range of around 3 - 45 mfd. and is connected to a start or extra winding continuously.

If you have connected the extra winding to the line connection on the cap or it is disconnected and the motor runs it will overheat.

Best test is to use a clamp on ammeter and check the current draw against the nameplate.
 
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Old 08-18-13, 09:08 AM
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Gotcha. The cap which initially went bad is a run cap I believe. It was rated @ 7.5mfd @ 440VAC (the same as the fan side of the dual cap). I think the definitive answer for me will be when I do an amperage check. THX.
 
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