Air conditioner humming outside but I have shut off the breaker


Hi,
I went out into the yard this evening and heard my air conditioner humming. The unit hasnt worked properly since we had a major power outage and so the only way to turn it on or off is at the breaker. I removed the wires going into the breaker but the unit is still humming. I openned the unit and the only power wires I can see are the black/white/ground. It is a very old sears model and I cant find any other shut off switch. What's going on!! Should I be concerned about the humming and if so, how can I completely remove the power to the unit without getting an electrician involved. I even tried going breaker by breaker to see if there was a wire touching but nothing stopped the humming
Thanks
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snipped-for-privacy@hotmail.com wrote:

You apparently did not shut off the right breaker. Remember that your furnace is not likely on the same breaker as the A/C unit. The A/C unit should have a 220V breaker and there should be a shutoff in the immediate area of the unit.
--
Joseph Meehan

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Thanks for this. It is definitely separate from my furnace. Im sure I have the right breaker though as it was the 220 and it stops the unit from actually running. I even pulled the breaker right out after pulling the wires. Would there be a separate power source for the heater? Just wondering if that is what might be humming. The panel of the unit (outside) notes that I need to leave it on for 12 hours before running the air if its been shut off, so Im assuming it has some sort of heating source for the fluid.
Thanks again
Joseph Meehan wrote:

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As was mentioned already, it's the low-voltage contactor you're hearing. The fact that it's buzzing, along with the fact that you had to shut down the 220 breaker to get it to stop, means that the contactor is getting power and calling for the A/C to run. If it were my system I'd be wondering why this is the case -- I'd probably start with the thermostat.
The contactor is powered by the same low-voltage transformer that powers your air handler (usually the furnace). It isn't really hurting anything to be on-- it takes very little power.
-Tim
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Thanks Tim. I tried shutting off every single breaker (including the line where the thermostat is attached) and none of them stopped the humming. I pulled out each of the wires (one at a time) from the contactor and it still hummed. Perhaps I'll try pulling the cold switch wire on the thermostat and see if that will stop it. My only concern was really that this buzzing had just started and that if it was a short, there would be the potential for a fire??
Thanks again
Tim Fischer wrote:

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If you've disconnected all wires to the contactor and it's still humming, I'd probably call a paranormal expert or a bee/wasp/hornet guy <grin>
-Tim
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This is what Im getting at. Its really odd that if I have all the wires out, it still hums. So Im wondering whether there would be a separate power source for the fan on the unit that is giving power to the thing. In fact, I had bees living underneath the unit this summer and had them killed off. Last night when I went out to look at the contactor, there were small worms crawling on the points - still alive, so there wasnt much power going to them but I wonder if they have shorted something.
Im off to get my palm read and maybe that'll help.
Thanks
Mano Tim Fischer wrote:

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wrote:

In my house, the outside AC unit has a separate electrical connection to the meter, and does not depend on the main panel. This normally makes no difference since turning off the main panel would prevent the 24VAC control voltage from getting outside. I guess it could still run if the contactor got stuck.

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Around here that's a code vio -- the fire department wants a single place to kill power in the entire building. Unless, of course, you have a shutoff out by the meter (we don't).
-Tim
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wrote:

I wasn't here when the house was built (about 1969). Maybe that electrician wanted to save some money (100A panel instead of 150A, and a little less wire). This does provide a disconnect next to the outside unit (the gas meter is there too). Maybe it would be better to have it routed through the main panel (although that would require a larger panel). I suppose it would be expensive (If I did have it done, it could be time to add AFCI breakers).
Inside, I have a 100A main breaker, 11 20A 120V breakers, and 3 30A double-pole breakers (stovetop, oven, dryer). All control things other than the A/C which has a 50A double-pole breaker outside (and another thing, the unit says not to use more than a 30A breaker).
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Joseph Meehan wrote:

Why not put the AC and the furnace on the same breaker? Course my furnace was electric so the power supply was 220 at 100 Amp. I just extended the line to where I wanted the AC unit and put the box and AC breaker there. No reason to use separate lines since the AC and the furnace can't run at the same time.
Course if you have a gas furnace and a 120V line that's another story.
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George E. Cawthon wrote:

My only concern would be what size breaker was specified for the A/C. If it specified a 50 amp breaker you are not protecting it (any the wiring if it was sized to 50 amp) with a 100 amp breaker and that would not be good.
It has been my experience which does not include electric furnaces as I live in an area where gas is cheap, that furnaces are 120V devices.
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Joseph Meehan

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Joseph Meehan wrote:

The first concern is duly taken care of as the 100A breaker is at the panel and a 30A breaker is at the end for the AC.
Lots of electric furnaces in the Northwest but may not be in many other places, that is why I specified that I had an electric furnace. Electric furnaces are usually 240 V, otherwise you would need huge amp breakers.
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On 3 Oct 2006 17:10:16 -0700, snipped-for-privacy@hotmail.com wrote:

My furnace has a seperate breaker, and on the furnace is the 'controler'. Since I have a heatpump/AC unit, I would guess in your situation, the controler is activating solenoids and relays, and that's what is humming.
Get a professional, you might find someone to help real cheap by networking. Check with your church members, coworkers, etc.
Good luck,
tom @ www.CarFleaMarket.com
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The 240 volts that power the condensing unit is not the power that energizes the contactor in the unit. The contactor, which is the thing that would be humming or buzzing, is 24 volt and powered from the air handler (blower)

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Probably the contactor. When the furnace indoors is calling for cooling, it sends a 24 volt signal to the outdoor unit.
To silence this, change your thermostat from "cool" to "off".
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Christopher A. Young
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It's best if you can read the whole thread before posting. We've already ruled this out...
-Tim
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