Hello, I have a Janitrol AC system (2 1/2 ton)
I turned the unit off at the circuit breaker, in order to replace the
disconnect box next to the unit. Someone bypassed it, when it burned a
With the circuit breaker off, I hear a low humming from the compressor
area. Is this normal?
Thanks in advance!
That depends upon where your control transformer is located. If it's in the
outdoor unit, then no, it shouldn't be making any noise at all -- unless
it's not really off. You'll find that out pretty quickly when you start
breaking connections <G>.
If it's in/near the indoor air handler (common), you need to turn off the
breaker to that, also. (It might even be on a different circuit - like
mounted on the wall near the air handler - check that, and make sure it's
OR... you've got musical bugs/rodents inside the unit.
Why didn't the stoopid SOB replace it when it burned???
If its humming with the breaker off, either you didn't turn off the correct
breaker, or it forgot the words. I would very highly recommend that you
check with a meter before sticking your fingers in there, unless you are up
for being nominated for a Darwin Award.
I would say you are just hearing the contactor (another name for a large
relay) humming. It is what switches on power to the compressor when the
thermostat calls for cooling.
The thermostat is most likely powered by a transformer located in the air
handler (which is on a different breaker). When the thermostat calls for
cooling it activates the contactor by sending 24VAC through the two small
wires that go to the outside unit. Those two small wires, or a wire pair,
supply power to the contactor coil
Some contactors make a humming or buzzing sound depending on the age and
state of wear of the contactor.
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