My A/C unit won't turn on. It just buzzes

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Old 07-29-12, 07:02 AM
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My A/C unit won't turn on. It just buzzes

Hi folks,

I will go ahead and thank everyone in advance for any help.

Last night I realized my A/C was not working properly. I checked the thermostat and the temp readings confirmed. I went and checked breakers and all work on properly. I then cycled both sets of breakers (main box and A/C unit box) and tried again, but with not luck. I noticed an electrical buzzing sounds and nothing else.

I came in and did some research on the problem and wound up on this site, which makes me think it is likely a capacitor problem. Being as it was 1130 at night, safety reasons (lack of light and being tired) made me decide not to play with electricity until the morning. (Luckily i have 2 A/C units and i could just sleep in a guest bedroom).

Well, this morning i pulled off the panel, and got to the Capacitor and it did not seem to be bulging. I'm not sure i would call it flat topped, but the rim was still sitting higher than the center of the top. The contactor also seemed fairly clean, with just a little corrosion on the leads going to it.

I closed it back up (i was just checking for capacitor bulging), turned the power back on, and tried again (maybe for just dumb luck purposes), and nothing had changed. I still had a buzzing sound and no operation.

I then followed some other (albeit less safe) advice, to get it into its buzzing mode (Thermostat running and power to A/C unit) and give the fan a little boost start with a stick. I did this with a wooden pencil (with safety glasses and work gloves on), and the fan started powering itself without a problem.

Is it possible that the capacitor is bad without bulging? I am not sure how to check if it is leaking or not. I have a cheap-o craftsman multimeter, but have never had the reason to use it. It does have a capacitance setting on it.

The A/C unit is as old as the house (almost 4 years) so i did not expect to be having appliance/electrical problems yet.

Once again, any help is extremely appreciated. I really prefer to do things myself when i feel that i can, and this seems like something i should be able to do fairly easily.



Also, if it is the capacitor, and tips on how to discharge it, and verify it is discharged with my multimeter (my multimeter Digital Mini Multimeter- Craftsman-Tools-Electricians Tools-Multi-Meters & Meters)

Thanks again!
 
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Old 07-29-12, 07:09 AM
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Can you post a picture of your capacitor? Also, yes, it is possible it failed without bulging. I would verify voltage into the contactor and out to the compressor and fan motor using your multimeter.
 
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Old 07-29-12, 07:27 AM
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Yeah, I will go take a picture of the capacitor here in a minute when i find my camera.

Is there much of a point of verifying the voltage from the contactor to the fan, seeing as when i gave it a bump it ran fine? could that be some sort of voltage bleeding issue or something?

It may take me a little bit to figure out which leads go where on the contactor. The wires are bundled and i think they all ran as a bundle into the unit before splitting off to individual components. I should be able to verify voltage TO the contactor though
 
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Old 07-29-12, 07:33 AM
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I missed that you started the fan by pushing it with a stick. This is an indicator of a failed capacitor.
 
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Old 07-29-12, 07:44 AM
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I tried to take a few pictures, but this is the only one that came out ok. Of course the electrical part of this setup is between the center of the unit and my house.

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Old 07-29-12, 07:46 AM
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replace your capacitor....................................
 
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Old 07-29-12, 07:48 AM
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Will Do!!

Do you have any tips on how to discharge the capacitor so i don't shock myself taking it out? Best i've seen is using an insulated handled screwdriver, but im not sure how i will touch all 3 sets of leads simultaneously. This is my first time playing with a capacitor of this style

Thanks again for the help bud!


p.s. Did you see something in the picture that told you to replace the capacitor or just everything points straight at it?
 
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Old 07-29-12, 07:51 AM
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I would not worry too much... there is a small likelihood it will be charged... But use an insulated screwdriver and short across 2 leads at a time. You dont have to touch all 3 at the same time.
 
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Old 07-29-12, 07:51 AM
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I thought perhaps hvactech had missed the stick start part.

Good luck finding any place that's open on Sunday. We did have one that was open til noon back in VA but it was 20 miles away.

As to the visual ID thing....sometimes they don't show anything...but you go by symptoms. When you get it out and compare it to a new one, you may indeed see something amiss. IIRC the terminals should all be straight up and down...if the are splayed out it means the top is bulged.
 
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Old 07-29-12, 07:56 AM
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Good luck finding any place that's open on Sunday. We did have one that was open til noon back in VA but it was 20 miles away.


Yeah, luckily the high here in DFW today is a balmy 107 degrees. My luck that it would break on a Saturday evening. I figure i will just sleep in the guest bedroom (2nd A/C unit hits that area) and just not be at home much today. I should be able to hit up Grainger tomorrow and hopefully they have them in-stock
 
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Old 07-29-12, 08:20 AM
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Repair Manual shows the capacitor i need is:

CAP050550370RTS CAPACITOR 5/50/370V

Will any 5/50 370V capacitor work or should i stick with the specific part number?

I assume the 5/50 describes 5 uFarad and 50 uFarad on the different ports


been a while since i have taken an electrical class
 
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Old 07-29-12, 08:27 AM
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Yes....any with the right spec will work. You can go higher on the voltage also if necessary.
 
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Old 07-30-12, 08:46 AM
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Replaced the capacitor today when Grainger opened and the unit came on like it should


After i verified it was working, i turned off the thermostat and killed the breaker (only the one at the unit, not at the breaker box) so that i could close up the paneling. After i closed it up, i flipped the breaker and turned the thermostat back on and once again, it did not come on.

I turned the thermostat back off, turned off BOTH sets of breakers this time, then flipped both sets back on (Breaker Box then Local AC breaker) and kicked the thermostat back on and everything worked this time. I feel the AC cooling too so i know the compressor is kicking on as well as the fan.

Could my failure in there just be not properly cycling breakers or is there possibly another underlying problem?

Thanks again for all the help... getting me this far has been a HUGE help, and im hoping that everything is working right now and it was just a breaker cycling issue.
 
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