Furnace fan issues


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Old 02-25-09, 09:20 AM
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Furnace fan issues

I recently purchased a house and the fan on the furnace constantly runs. I checked the thermostat wiring and it seems correct. it is a two wire system with a separate air conditioning unit that was installed at a later time. The fan continues to run even when I disconnect the thermostat. Can I assume that something is wired incorrectly between the air and the furnance?
 
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Old 02-25-09, 09:50 AM
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Please post the make and model of the furnace, which can be obtained from the rating plate for the furnace, usually found in the burner compartment.
 
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Old 02-25-09, 09:51 AM
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What do you mean by "its a two wire system" ? Are you saying you have a furnace with an indoor A/C coil and a condensor outside operated by one stat that only has two wires hooked up to it ?
 
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Old 02-25-09, 04:50 PM
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Or, do you have a 2-wire, heat only thermostat? And a separate thermostat for the a/c? If you have a separate a/c stat - what is that set on? Mention all settings. For instance - it might be possible that on the separate a/c stat, the stat is set to a temp below current room temperature, and the outside a/c compressor-fan condensor unit's disconnect is shut off, but the temp setting is still calling for the furnace fan to run, since the furnace fan is what delivers the cold a/c air when that stat comes on. And maybe it is on! The reason this could happen is the fan's "G" wire is twist-tied together down in the furnace, in parallel between heat and a/c.

If the above is not it: And if you just bought the house -unless they are very firm about some "as-is" clause, you might contact the realtor or seller and ask them to see if the ex-owner can shed some light on what they might know. It's worth a shot, anyway.
 

Last edited by ecman51; 02-25-09 at 04:58 PM. Reason: added more
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Old 02-26-09, 11:57 AM
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thanks for the reply. we have only one stat. but i will cleck the wiring for the air conditioner to see if that is the problem. i did kill the power to the furnance and removed the wires from the stat. then turned the furnance back on and tne fan still ran.
 
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Old 02-27-09, 04:57 AM
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As Seattle requested - what are the make and M# of the equipment ?
 
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Old 02-27-09, 03:04 PM
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Originally Posted by chuckcain
thanks for the reply. we have only one stat. but i will cleck the wiring for the air conditioner to see if that is the problem. i did kill the power to the furnance and removed the wires from the stat. then turned the furnance back on and tne fan still ran.
I thought I 'nailed' this one. (Same scenario as I had in commercial building I took care of years ago) How disappointing, for both you and me. I have not been doing well, in the guessing dept. lately, it seems.

I do know this much -something is not right the way you are explaining the stat having 2 wires then, if you have both central a/c and heat. Does that stat then control both the heat and a/c? We need to get to the bottom of that issue. Can you answer dun11's question then? And fully describe the stat.
 
 

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