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
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.
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.
Joseph Meehan wrote:
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.
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??
Tim Fischer wrote:
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
Im off to get my palm read and maybe that'll help.
Tim Fischer 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.
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).
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.
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
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.
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.
On 3 Oct 2006 17:10:16 -0700, email@example.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.
tom @ www.CarFleaMarket.com
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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