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:
"traveller2k" wrote in message
ups.com...
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.

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