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Old 09-15-2009, 06:28 PM   #1
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Lennox Ac Fan


My Lennox ac fan wont turn on when the AC unit comes on. I could hear the ac unit outside come on but the fan wont turn on inside. The control board shows two green light simultaneously blinking. The fan does come on when the its set to "on" but not when its set on auto. The ac fan sometimes kicks in when the fan is set to "on" for few hours. If I set the unit on heat everything including the fan works great. I think I might need a new controller board. Please Help Thank You

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Old 09-15-2009, 06:39 PM   #2
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Lennox Ac Fan


What is the model and serial # of the furnace? I am a Lennox tech.

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Old 09-15-2009, 06:44 PM   #3
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Lennox Ac Fan


what type of a system is this. Heat pump. or other fuel furnace with A/C. I would first start with the T-stat. In A/C mode the fan is energized at the T-stat. Since you have fan oporation when switched to the on position, that means that the board is sending the signal to the fan when it is told to. It is hard to tell without putting a meter on things but that is where I would start
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Old 09-15-2009, 06:44 PM   #4
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Lennox Ac Fan


Yuri,

Thank You for your response: The Model # is 80MGF3/4 100A-1. I have to find the serial number I will get that to you in a few hour since I am not at home right now.
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Old 09-15-2009, 07:19 PM   #5
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Sounds like you need a new circuit board. The cooling relay is faulty. The replacement board may be a retrofit (99% certain) and can be difficult to install if you are not familiar with schematic wiring drawings etc. Try Cozyparts.com for Lennox parts and the serial number is important. You may want to call a Lennox dealer. The new board has adapter cables and may require some wiring alterations. I have seen lots of them.

Last edited by yuri; 09-15-2009 at 07:26 PM.
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