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-   -   Blower Motor Problem (http://www.diychatroom.com/f17/blower-motor-problem-50365/)

curranelectric 08-06-2009 11:48 AM

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.

hvaclover 08-06-2009 02:42 PM

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

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

Yoyizit 08-06-2009 03:31 PM

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.

hvaclover 08-06-2009 05:11 PM

Jeeze yoyzie...you sure love your numbers:eek:

Yoyizit 08-06-2009 05:19 PM

Quote:

Originally Posted by hvaclover (Post 311310)
Jeeze yoyzie...you sure love your numbers:eek:

Ur Momma'!

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

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.

hvaclover 08-06-2009 07:04 PM

Quote:

Originally Posted by Yoyizit (Post 311315)
Ur Momma'!

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

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:laughing:


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