Which is the A/C motor start capacitor?

I posted about my A/C fan motor getting stuck when it first turned on, and everybody pointed to the start capacitor. I have found three capacitors just under the top case. Are any of these the start capacitor?
1. GE 21L3638RA -- does not google. 30uF 440VAC 60Hz. Biggest of the three. Oval and metallic finish. 2. GE 21L3515 -- Comes up as a power capacitor. 15uF 440VAC 60Hz. Medium size of the three. Oval and metallic finish. 3. Aeromet II MRP926507 -- I think this is it but the brand comes up for motor run capacitors too. 7.5uF 370V 50/60Hz 70C.
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On Mon, 08 Oct 2007 22:02:02 +0000, Adam Preble wrote:

What is the motor ID number? What kind of a/c unit? Model? Unless I've damaged some brain cells since I worked on this stuff for a living in the early 80's the highest value cap is the start cap. Or was it the lowest value? Or does the value make no difference? Hard to tell with little info you've given.
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Much of the identifying information is worn off. Here is a picture of the motor label:
http://www.adampreble.com/~rocko/images/DSCN2492.JPG
I can't make any sense of it, but the schematic towards the right refers to a capacitor. I have a brown wire with a white line along it that goes to the Aeromet II capacitor: 7.5uF 370V. That is the smallest capacitance of the three.
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On Oct 8, 7:36 pm, Adam Preble <adamDOTprobleATgmailDOTcom> wrote:

Usually the round one is the start. Make a diagram of the wires, remove it and take it to a motor shop. They can test it for you.
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the
to
to
of
Oval, round, etc... makes no dif. BTW, its a *run* cap.
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"Adam Preble" <adamDOTprobleATgmailDOTcom> wrote in message

to
Why don't you call in a professional to straighten out this mess? The motor clearly calls for a 10 MF cap. Which is a value that you didn't list. That tells me someone that *doesn't* know what their doing has been messing around with your unit. So it looks like it's time to call in a professional and get this shit straighten out once and for all.
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and
Medium
You were in the trade and you don't know??? This is just too funny, especially since you have *tried* to argue with me on HVAC issues.
X to hvac as they like a good laugh.
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Adam Preble <adamDOTprobleATgmailDOTcom> wrote in

I forgot to mention that this capacitor is the smallest of the bunch and is in a cicular, light grey, plastic housing.
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Cut ALL the power to the unit and then trace the wires.
Use a cheap VOM to help.
"Adam Preble" <adamDOTprobleATgmailDOTcom> wrote in message

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On Oct 8, 5:02 pm, Adam Preble <adamDOTprobleATgmailDOTcom> wrote:

(etc)
I should update that I replaced the 7.5MFD capacitor with a 10MFD capacitor. The fan started up right away. However, I still think the motor is on its way out. I checked on the unit when it was running a cycle later on and the fan motor wasn't working; the fan turned freely, but I could hear the compressor running. I was getting a 60Hz hum out of a panel where many of the wires meet up at the top of the unit.
Today, I turned it on after an evening with it shut off at the thermostat. The fan was turning very slowing and the motor was giving off a hum. It did resist when I turned it manually, but this time that didn't do anything to get it working.
I'll double check my wiring but I'll also check on that panel because I assume there's some stuff in there that can croak on me. I wanted to also discharge the run capacitor and try it again. Worst case, a new motor can be had for about $60, but it'll take me a few days. I'd like to try to get the motor as isolated as possible first.
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snipped-for-privacy@gmail.com writes:

You should find a wiring diagram of the unit and see if the fan is even supposed to be running at that point. The fan may be turned on by a pressure switch in the high side of the refrigerant system, instead of always running when the compressor is running. Or it might be a multi-speed fan, where one speed is working and another is not.
The fact that there's a hum doesn't mean much in itself. Transformers hum, relays hum, and the presence of hum doesn't mean that the fan should necessarily be running.

Well, is it a multi-speed fan? Is power applied to it?
    Dave
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snipped-for-privacy@cs.ubc.ca (Dave Martindale) wrote in writes:

even
The only things I have found are: 1. A spare wiring diagram for the motor on the motor. It had worn off except for the top that described it as such. 2. Some freon charging tables that were just inside the lid. I didn't see wiring with it. 3. The wiring diagram on the rusted label I posted earlier.
I don't think I have the whole system here, but I can understand it would really come in handy. I saw it run at a reduced speed earlier as I was working on it before it managed to speed up. The motor sounded terrible, and I'm inclined to replace it even if it something else is contributing to the problem.
Also, seeing it eject some smoke really sent the message home.

The motor itself was humming without anything happening though. It was definately the motor.

Oh by "slowly" I meant that it was going a revolution every 3 seconds or so and it was doing it with a jitter like it was stuck somewhere in the cycle. That being said, I did see it move at some speed between that and full on. But the magic smoke convinced me the fan's a goner.
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responding to http://www.homeownershub.com/maintenance/Which-is-the-A-C-motor-start-capacitor-256446-.htm cinco2010 wrote: three item are motor run capacitor,not start capacitor Adam Preble wrote:

-------------------------------------
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On Aug 25, 5:14am, zhanjixiang_at_hotmail_dot snipped-for-privacy@foo.com (cinco2010) wrote:

Sounds like a fan motor problem but it would be good to make sure you have a single speed fan on the outside unit and what other conditions would prevent it from being on. What's the year, manufacture, and model number of your unit?
On heat pumps there is sometimes a humming from the reversing valve when the unit is not running. Just mentioned that so you know there can be other legitimate sources of humming in the outside unit. I find it pretty hard to detect/distinguish any other humming when the compressor is running.
On the large majority of basic units the contactor (big relay) supplies power to the fan and fan run capacitor. It is the same thing that supplies power to the compressor. If the fan motor has any start circuitry it will be internal to the motor.
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cinco2010 wrote:

http://www.homeownershub.com/maintenance/Which-is-the-A-C-motor-start-capacitor-256446-.htm

You are responding to a question that is almost 3 years old. Do you think an answer is still useful? Do you think the A/C is still not fixed, 3 years later? Do you think the person who posted the question is still around?
You are responding to a usenet newsgroup. Maybe you could find out what usenet is. Homeowners' hub is a parasite that steals the work of others. If you don't want to figure out usenet, I suggest using google groups.
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