Carrier furnace troubleshooting


Old 02-16-11, 06:28 PM
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Carrier furnace troubleshooting


New to the forums, hope to learn much. I AM reading the archives trying to get some help too.

One of my two furnaces has essentially stopped working. Over the last week it has worked and required resetting to keep heat coming. At that time it was only blowing unheated air.

Now, it isn't blowing at all, and despite the thermostat being turned off I am getting a loud electric hum coming from it in the attic. The hum lasts about 30 seconds and has about 3-minute intervals.

In the attic the box which houses (presumably) the transformer is just buzzing.
I found the local power switch for the electrics (a 2-switch panel: one for each floor) and shut it off which halted the electrical buzz. I've not heard the loud hum since.

I picked up a multi-meter but haven't had a chance to get back in there to see what's going on.

I enjoy projects, and as this is our first home, I'd rather gain some experience before dropping the service call fee and being in the dark (so to speak).

Any thoughts would be greatly appreciated.
Old 02-16-11, 07:08 PM
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i need to make a correction.

The second furnace for the upstairs was the one with the noisy box on it. That unit is functioning just fine.

The loud hum (coming at intervals) was coming from the seemingly quiet unit. I managed to wait on the ladder until I caught it.

It sounds like it's right inside the area where the burners are. Quite loud with a fine vibration to accompany it, then it simply stopped. I can see the pilot is lit.
Old 02-17-11, 02:53 PM
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well, first off you are going to need to get to the unit so we can do a little troubleshooting. Pictures would be nice, and so would a model number.
Old 02-17-11, 04:24 PM
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I'd start by taking the cover off the burner compartment. Find the rating plate and copy down the model number and manufacturer of the furnace from the rating plate.

Post that here.

Then carefully observe the sequence of events that occur when you turn up the thermostat, and post that sequence here. You may need to observe that several times until you can follow that sequence accurately and completely.

And listen carefully to identify what is doing the humming, and post that here as well.

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