Forced air furnace will not turn off properly.


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Old 10-04-10, 05:33 PM
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Forced air furnace will not turn off properly.

I have a 20 yr old forced air furnace that will not turn off once the temperature has hit what was set. It will turn off if I quickly turn the fan switch from auto to on, then back to auto. I did try replacing the thermostat, with no help. I am sure I am leaving out info, not familiar with the heating system as I probably should be. thank you
 
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Old 10-04-10, 07:35 PM
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We need more info.. Make and model of the furnace. Is this a furnace or air handler? (You have it posted in heat pump/electric heat)
 
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Old 10-05-10, 06:13 PM
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My apologies, should I repost or can this be moved?... it is a forced air furnace. The make (manufacturer?) is Inter-city products, and the model # ( I didn't see a model name on the sticker) is NBCM036XKB2.
 
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Old 10-05-10, 07:04 PM
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I got you moved, what brand is on the front cover? I tried looking for the model #, and came back empty.
 
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Old 10-05-10, 07:50 PM
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Picasa Web Albums - Dave

Picasa Web Albums - Dave

I hope the links work, they are pics of the label on the front. thank you.
 
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Old 10-06-10, 11:53 AM
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You have an Air Handler, not furnace.

I am not able to find anything, chances are you may have a relay.. Take a photo of the wire diagram of the unit.

Make sure the t-stat switch is set to "AUTO", if so, then find the G wire at the air handler, and remove that and see if the fan stops.
 
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Old 10-07-10, 04:12 PM
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Pic of the wiring diagram.

Picasa Web Albums - Dave

I did check the switch, it is set to auto. As for the G-wire, it is spaghetti in there, and not sure which one to unplug. G is green at the thermostat...would it be the same at the air handler?
 
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Old 10-07-10, 04:31 PM
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Yes........................................

Looked at your schematic. Problem likely at 4 in relay where black wire continues to blower motor. It is stuck. Points inside likely arced and are being glued together. Try rapping on that relay (trace the black wire out of the blower motor back to some box - the relay), and rap on that box with the butt end of a screwdriver and I bet it shuts off when you do. If it does, buy new relay.
 
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Old 10-18-10, 06:03 PM
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I think I found the correct part. $63 not a bad price to possibly avoid a rather large service call bill. Can you please tell me how difficult it is to replace? Doesn't look ver gard. 2 screws hold it in. Only thing that concerns me, the 4-5 wires that connect to it. Assuming I cut poower at the box, is there anything else I need to worry about? This is the part I believe:

24 Volt Blower Control Relay. (InterCity Products): American HVAC Parts

thanks!
 
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Old 10-18-10, 06:52 PM
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If you cut the power...... no I really can't think of a problem, except perhaps yanking wires out by the roots.

Only you know best how they are attached. Is there a 4 wire jack that you first spread the side plastic a little bit to open the lock for the jack?, and then slip it off? Or are 4 wires plugged in separately?

It will really be obvious when you get the new part, if you are at all in the dark now.
 
 

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