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2 Posts

Posted - 10/09/2005 :  5:08:02 PM  Show Profile  Reply with Quote
Furnace - Lennox G12
When either AC or Heat was engaged blower started cycling on and off about every minute and then just quit. Does not operate when selecting blower on at thermostat. When thermostat is set to "blower on" or AC and you turn power on to furnace you get a loud click from the relay (original part #p-8-8479, your #3827601) and then the relay hums.

Edited by - Buchanan on 10/09/2005 6:13:05 PM


1499 Posts

Posted - 10/11/2005 :  05:27:40 AM  Show Profile  Reply with Quote
Since we are entering the heating season I would advise that you have the furnace inspected by a professional heating company before attempting repairs on the blower.

The Consumer Product Safety Commission Urges Seasonal Furnace Inspection to Prevent CO Poisonings

The technician should carefully inspect your furnace checking the burners for rust, the heat exchanger for safety ie. cracks, rust holes and in the case of G12's with the Duraglass heat exchangers that the coating is still in good condition. Duraglass heat exchangers have a porcelain type coating. If the coating is deteriorating and flaking off and covering the burners carbon monoxide levels can exceed safety standards and if allowed to continue could lead to sooting and blocking that chamber. Also backfiring and flame roll out could result. Call a company that tests using a co/combustion meter checking the undiluted flue gases before it enters the draft hood.

Gary Reecher, CM
HVAC Service Tech

Please have your furnace inspected annually by a qualified service technician. Have them test the flue gases for proper combustion and carbon monoxide production.

Get a good Carbon Monoxide Alarm. CO concerns are not just for the winter but 24-7.
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2 Posts

Posted - 10/11/2005 :  12:33:41 PM  Show Profile  Reply with Quote
Thanks for looking at the thread. Furnace was inspected last year - no problems. I also have a CO detector which gives constant readouts of any CO detected in the air. Now back to my problem. I checked and I do have power on terminals 2 & 3 of the relay so it is probably OK, but is is normal to be humming. Could it be the capacitor or do you think it's the blower motor itself.
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5983 Posts

Posted - 10/11/2005 :  3:29:25 PM  Show Profile  Reply with Quote
If your furnace fan motor has a run capacitor (not all G12's do), check and make sure it is good.

If you do not have a capacitor checker, you can get an "educated guess" about the usability of the capacitor using an ohm meter. If the capacitor checks bad with this method, it is probably bad...if it checks good, it may actually be weak. Here is some help if you have to use an ohm meter:

If the capacitor checks good, check and make sure that the 115 VAC power to the motor is not being interrupted by the relay or other controls. If power is applied to the motor, and the motor quits, and you know the capacitor to be good, then you need to be suspicious of the motor.

Also be mindful of the fact that the motor should have only one speed winding at a time energized. It is doubtful that more than one winding at a time is being energized unless someone has been working on the furnace and put a wire in the wrong place.
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