I have an air handler in the attic. It continues to make a humming sound even when the thermostat is off and the rooms have been heated to the proper temperature. It shuts off if I switch the breaker but otherwise continues running.

Is the blower running OR is this just a HUM noise.

Well if you mean blower as in blowing air through the vents no, but it sounds like some type of fan is running in the attic it sort of sounds like the hum of a plane from far away even though no air is blowing through the vents. This happens even when I turn the mode from heat to off on both thermostats.

Since you did not provide a model number for the air handler as you call it can you get the exact model number now. Also what kind of system? Heat pump, gas furnace? I will try to look the components up to see what could cause the noise.

Yeah maybe I am using the wrong word but it's an air conditioner and heat pump system. The part in the attic with the coil and blower assembly continues to run even when my house does not need to be heated. In fact once I turn the temp down on both thermostats the blower fan shuts off but the unit kicks on harder. So I have been turning it off at the breaker box... there in the breaker box the name next to that breaker is called air handler, which is why I am also calling it the air handler... But the heat turns on. My house is heated and the outside fan also turns on. Whatever it is up in the attic doesn't shut off even when I set the thermostat to off.

Whatever it is up in the attic doesn't shut off even when I set the thermostat to off

Please provide exact model number for this unit.

Yeah its fv4b

Here are your wiring diagrams that list component parts. There is no way for me to tell from here what is making the noise except to guess and that accomplishes nothing.

http://www.docs.hvacpartners.com/idc...wd-fa4c-02.pdf

Install

http://www.docs.hvacpartners.com/idc...im-fv4b-02.pdf

Well it has to be the blower inside the thing making the noise right? What else would? Does the coil make noise?

Does the coil make noise?

NO

I just turned everything off and then turned everything back on again and it appeared to begin working correctly on its own.

I hope it keep working for you without the noise.

It's not a noise. I think the blower runs because the unit thinks its overheating and is cooling it down before turning off. So I probably have to do something to the limit switch. Is there a reset button or does it have an auto reset?

It could be cycle or auto reset. It could also be the low voltage transformer making the noise or vibration since sometimes the laminated plates work loose and vibrate. If that is the case replacement of the transformer will cure the noise.

The only real way is to go to the unit and listed to track the noise down.

If my thermostats are set to off shouldn't the thing eventually turn off and how long should it take

If there is no call for heat usually the furnace and blower will be off in no more than 2 minutes.

I think that it is my time delay relay because the indoor blower is not shutting off

It very well could be or the thermostat is set to on instead of auto at the blower switch on the thermostat.

Ah OK well I have a carrier guy here looking at it now. Wish he spoke English

He pulled the yellow wire and said that my auxiliary heat was coming on and not turning off and that I have a bad control board.. . The thermostat was still saying auxiliary heat was on/ on the thermostat display.. .