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Old 08-06-2009, 11:48 AM   #1
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Blower Motor Problem


I was called out to a moble home that the blower motor stopped running. I went to the force air furnace unit and jumper it to start the blower motor and it started to hum. So I check the Run Capacitor and it was good. So I took of the Blower assembly out and took it to the shop. I wired it up to check it and it worked great in all speeds. So I brought it back and hooked it up and it did the same thing....Hum. Thought it might be the fan relay so i by passed it and it did the same thing. Then I wired it up again to plug it in to a wall plug other then the dedicated circuit for the Air Handler the same thing happen. Then I went to the Moble home next door and plug it in there and it ran fine. The outside 220v compressor works fine so I know there is no problem there. I check all the connections in the panel box to make sure they are tight and they were. Could it be a bad neutral coming from the utility company to when I switch the blower motor on it drops out just enough to make it not start? The strange thing is why it works everywhere but in the home.

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Old 08-06-2009, 02:42 PM   #2
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Blower Motor Problem


God does not like electrician working on furnace J/K guy.

You check the voltage of the fan supply? Sounds like a voltage drop to me.

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Old 08-06-2009, 03:31 PM   #3
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Blower Motor Problem


High resistance upstream? Load the wiring at the (120v?) blower end with a 10A 120v hairdryer. 20' of #14 copper wire should cause a drop of ~ 1v.

Using the method I found a 0.5 v drop across a wirenut that was barely holding its 3 wires. When I removed the wirenut the stripped end of the wires that were in it were still straight, rather than having some twist in them. This implies a very small contact surface area.
What I missed was an outlet upstream with somewhat loose screws, because I didn't have a helper pushing on this outlet while I watched what the hair dryer did.

BTW, good relay contacts that are closed will have less than 30 mV across them at rated current. Bad, >100 mV.

Last edited by Yoyizit; 08-06-2009 at 03:34 PM.
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Old 08-06-2009, 05:11 PM   #4
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Blower Motor Problem


Jeeze yoyzie...you sure love your numbers
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Old 08-06-2009, 05:19 PM   #5
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Blower Motor Problem


Quote:
Originally Posted by hvaclover View Post
Jeeze yoyzie...you sure love your numbers
Ur Momma'!

". . .when you can measure what you are speaking about, and express it in numbers, you know something about it. . ."

I guess I and the taxpayer paid good money for me to learn numbers, so I'm trying to get my and their money's worth.

One of these days I'll find a real job.

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Old 08-06-2009, 07:04 PM   #6
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Blower Motor Problem


Quote:
Originally Posted by Yoyizit View Post
Ur Momma'!

". . .when you can measure what you are speaking about, and express it in numbers, you know something about it. . ."

I guess I and the taxpayer paid good money for me to learn numbers, so I'm trying to get my and their money's worth.

One of these days I'll find a real job.
I got ur Daddy first

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