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Old 11-17-2011, 06:40 PM   #1
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Lennox 80MGF3/4-100 Blower


First post, but have read quite a bit here, and still have an issue and question.

First I have a 1996 Lennox 80MGF3/4-100A-7 Furnace
We recently, end of September, bought our house and have intermittently used the furnace with no issue.
The last few days the furnace didn't want to run correctly. The diag codes signaled Limit Switch Open (Flashing, On). After much problem solving, and testing. I had the blower panel open and saw that even the the system was firing correctly, the blower motor/fan never started up. After resetting a couple times I decided to give the fan a little push and it started working 'normal'.

I have 117-120 volts going to the motor from the circuit board.
Everything else seems to be working fine, glad the Limit Switches working properly....

My question, is this something that the blower motor needs to be replaced or the capacitor, or both?

I spoke with a repair man, and as helpful as he'd been, he didn't say for sure one way or another(of course he wants to be paid to fix it for me) and said it could be the capacitor, but that it could just be part of the issue.

Anyone have any ideas, suggestions?

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Old 11-17-2011, 06:53 PM   #2
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try the capacitor first but it also could be the motor seizing from age.

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Old 11-25-2011, 11:44 PM   #3
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So far so good, new capacitor is working. Thanks for the help
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Old 11-26-2011, 12:22 AM   #4
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Originally Posted by MNPyro View Post
So far so good, new capacitor is working. Thanks for the help
The only way to tell what condition that motor is in, is to do a amp draw measurement on it. I would not expect to see much over 4 or 5 amps in the heating mode.Any more then that and it may be time for a new motor.
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Old 11-26-2011, 12:24 AM   #5
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Originally Posted by harleyrider View Post
The only way to tell what condition that motor is in, is to do a amp draw measurement on it. I would not expect to see much over 4 or 5 amps in the heating mode.Any more then that and it may be time for a new motor.
What tool, or meter, would I need to do something like that?
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Old 11-26-2011, 09:16 AM   #6
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Amprobe, clamp over wire amperage reading meter. At 15 yrs old it is time for a new motor as that is the life expectancy. The fact you had to give it a little push tells me it is stiff and seizing up. I work on LOTS of those furnaces and if you live in a real cold climate where it gets used a lot and has original parts then it may turn into a money repair pit soon and you may want to think about a new furnace. May need a circuit board and ventor fan soon if they are original. Any brand at that age will be in the same boat.
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Last edited by yuri; 11-26-2011 at 09:29 AM.
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Old 11-26-2011, 09:26 AM   #7
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Ack!! My eyes, MY EYES!!

Amprobe is cheap to boot, complete poo.

This Fieldpiece SC 46 is under $80 and will go a lot further.
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Old 11-26-2011, 09:32 AM   #8
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I still have one of these and it is probably older than you. LOL.

Beenthere probably has one too. Great in the Winter on rooftop units as it does not have batteries.
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Old 11-26-2011, 09:39 AM   #9
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What's this Winter you speak of?

Here go some of my meters: New SC 77, original stick (still working well) and some accessory heads.
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Old 11-26-2011, 09:49 AM   #10
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My hacienda, family pet, and block heater.
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Old 11-26-2011, 09:53 AM   #11
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Me.
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Old 11-26-2011, 10:04 AM   #12
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I am learning all about Texas from the TV shows.

COPS.

One Cop to the other: "What he do?"

My favorite show: American Hoggers

http://www.aetv.com/american-hoggers/
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Old 11-26-2011, 10:39 AM   #13
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I am learning all about Texas from the TV shows.

COPS.

One Cop to the other: "What he do?"

My favorite show: American Hoggers

http://www.aetv.com/american-hoggers/
Have you seen the one were its two um, well how should i put it.......welll they are a little top heavy females doing the catching?
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Old 11-26-2011, 10:50 AM   #14
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Yep. Some fine lookin ladies in Texas.
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Old 11-26-2011, 01:56 PM   #15
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I needed a new lennox blower motor,dealer item only,so I installed a new Ducane heat pump system.

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