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Old 06-11-2010, 01:33 PM   #1
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dual run capacitor


Is it easy to change out a dual run capacitor on a central A/C unit (Comfortmaker model # AG024)? Mine is outside the recommend range abd they want $300 to replace and it looked pretty easy when he was taking it out.

Tim

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Old 06-11-2010, 01:40 PM   #2
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Yep. Just wear leather gloves or it can zap you when removing it and label and mark the wires B4 removing them. They are marked. Herm, fan and common usually. Probably can buy one for under $50 at Graingers. Has a rating in volts and microfarads. Ie: 35 + 5 mfd at 370 Vac but some are 440 Vac so get the right one.

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Last edited by yuri; 06-11-2010 at 01:43 PM.
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Old 06-11-2010, 02:03 PM   #3
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How do I tell?
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Old 06-11-2010, 02:13 PM   #4
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Quote:
Originally Posted by timchi29 View Post
Mine is outside the recommend range
Keep the old one until everything is working; you can measure it several different ways if you have a DVM and a few other components.
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Old 06-11-2010, 02:46 PM   #5
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this is a common problem that HVAC companies make a killing on. My buddy got a quote of $250 for the same thing, it's absolutely ridiculous and highway robbery if you ask me.

the capacitor should have the voltage and dual uF ratings written on it somewhere. if it is bulging, that's a good indication, or if you have a digital multimeter that measures capacitance you can compare it to the listed rating. you can also hook up a multimeter in the highest resistance mode setting, and discharge the capacitor using a screwdriver and hook up the multimeter to it and the resistance should start at 0 and go up to infinity (usually 1 on the meter). Always hook the multimeter up from COM to HERM or COM to FAN.

You can buy them in any HVAC supply store if you know where one is in your area for around $10-$15. you can also buy them on e-bay for about the same price but will have to wait to get it shipped. Make sure you get the right kind, either oval or round and usually 35+5 370 VAC. 440 VAC will work find also, but the two numbers 35 (compressor uF) and 5 (fan uF) are the important ones and must match.

First, cut the power to the outside unit, the easiest way to do this is remove the large fuse that should be next to the unit. Cross the C or COM (Common) with the HERM (Compressor) and then do the same with the COM and the FAN (Condenser Fan) with a screwdriver to discharge the capacitor. Take a picture or write down the wiring, should be blue on HERM, brown on FAN and any yellows on the COM, but not guaranteed. Remove the old one and wire up the new one in the same way.

Last edited by NitroNate; 06-11-2010 at 03:00 PM.
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Old 06-11-2010, 03:08 PM   #6
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Nitro, what do you mean by cross? I am pretty handy (or will at least try something once) and haven't really messed around with A/C unit before. Could I just turn it off at the the breaker panel, unplug the 3 wires connected and then just plug it in to the new one?
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Old 06-11-2010, 04:29 PM   #7
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I looked at the capasitor and it's either has a mfd of 35/3 or 35/5 and unforuntely they make a 35/3 and 35/5 so I can't use process of elimination. The part # is M26P4435W03 from Aerovox and based on the 03, I am guessing it should be a 35/3, but their website (sheet 8) isnt showing a 35/3 or my part # so I am at a lost...


http://www.aerovox.com/pdf/AC_Motor_Run-8C.pdf
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Old 06-11-2010, 05:01 PM   #8
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Unfortunately Comfortmaker had some 35/3 and other companies use 35/5 so you may want to get it from an Comfortmaker dealer who can look it up for you.
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Old 06-11-2010, 05:11 PM   #9
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Unfortunately Comfortmaker had some 35/3 and other companies use 35/5 so you may want to get it from an Comfortmaker dealer who can look it up for you.
Shaking head.

I cursed Comfortmaker out more then once on a weekend for that.
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Old 06-11-2010, 05:45 PM   #10
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Originally Posted by timchi29 View Post
Nitro, what do you mean by cross? I am pretty handy (or will at least try something once) and haven't really messed around with A/C unit before. Could I just turn it off at the the breaker panel, unplug the 3 wires connected and then just plug it in to the new one?
Yes, you can turn the breaker off, but a capacitor will retain a charge even after the electricity to it is off. Touch the metal part of the screwdriver across the two pairs of terminals (com to fan and com to herm). this will discharge it before you go touching it and messing around with it. otherwise, you could get shocked.
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Old 06-11-2010, 05:54 PM   #11
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dumb question. How do you cross the the terminals with a screw driver?
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Old 06-11-2010, 06:37 PM   #12
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yeah you've got a 440 vac 35+3. search e-bay for 'capacitor 35+3'. there are plenty of them, you just won't find the same brand. i replaced my aerovox with a cheap generic version a couple of years ago and it's been working fine.
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Old 06-11-2010, 06:51 PM   #13
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Better to discharge it through a resistor, 15k, 2w.
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Old 06-11-2010, 06:52 PM   #14
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how do you do that?
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Old 06-11-2010, 06:57 PM   #15
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how do you do that?
You buy a 15,000 ohm, 2w resistor from Radio Shack and put it across the terminals, two at a time.
It discharges it in 3 seconds at a safe current level.

Caps don't like short circuits, the current level for an instant is extremely high.

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