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Old 08-07-2011, 08:06 AM   #1
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Lennox Furnace Issue


I have an old Lennox Furnace that's about 30 or so years old in a home I just bought. The problem is that when I turn on the AC some times all I hear is this clunking noise coming from the blower motor. When I looked closer the clunking noise is the motor starting for about a split second then turning back off. Some times the blower will get up tp speed for a few seconds then shut back off and some times it works just fine.

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Old 08-07-2011, 08:39 AM   #2
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30 years old, and showing problems, time to change. Was this not inspected by a home inspector before purchase of the home, or are you living in a rental.

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Old 08-07-2011, 09:41 AM   #3
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Welcome Jim DEnault, to the best darn DIY'r site on the web.

Not sure if its worth repairing given its age, but sounds to me like you need a new blower motor. If you do repair it, remove the motor and take it to a place like Grainger and they will match it as best as it can be matched.

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Old 08-07-2011, 10:04 AM   #4
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It is a belt drive motor and probably the starting switch is shot. Check the pulley on the motor and blower wheel to see if they are loose. Time for a new furnace IMO as the heat exchanger will have cracks at that age. Main blower wheel may have a loose hub also. Not worth spending $$ on. Less than 60% efficient, more like 50%.
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Old 08-07-2011, 11:43 AM   #5
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The Furnace was inspected. Heat exchanger is not cracked, has a good burn according to the HVAC Tech that looked at it. I plan on changing the unit in the fall, but if I can fix it for a few buck just so I can run the AC I will.
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Old 08-07-2011, 11:48 AM   #6
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Probably just needs a new belt drive motor if that is what it has. Try Acklands/Johnstones/Grainger.
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Old 08-07-2011, 05:36 PM   #7
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The Unit # is G12q3822 Serial # 5879E03237 Does anyone know if this unit has the Belt Drive motor that was mentioned? I guess I'm still a little confused by the Belt Drive Motor as the unit still runs sometimes.
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Old 08-07-2011, 05:54 PM   #8
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G12 has a direct drive motor. G8 the sister would have had the belt drive. May have a bad fan relay to turn the motor on or bad hub in the blower wheel itself or the thermostat is not energizing the G terminal properly. Need a experienced tech to catch it while it is doing it. If you plan to replace it in the fall I would do it sooner than later. Repairs are going to be $200-$400 depending on what is wrong etc.
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Old 08-07-2011, 06:13 PM   #9
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Do you know where I can get a fan relay?
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Old 08-07-2011, 06:43 PM   #10
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no. that unit is obsolete and I have not seen one in years. could also be a problem with the thermostat or even the motor itself. one of the windings may be shorting or opening up.
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Old 08-07-2011, 06:51 PM   #11
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I changed the thermostat so that's not it. It still acts the same way. Is there anyway to jumper the fan switch to see if it is in fact the switch?

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