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Old 04-06-2010, 07:22 AM   #1
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Motor runs slow


Greetings to all
I have a 4 speed Blower motor in my Central A/C air handler that seems to be running slow and not pushing the air as in the past. I did remove and inspect it and it is very clean and turns very freely. A test on the run capacitor which is 12.5UF showed it to be 10.6 so i replaced it and I have not seen any big improvement. ( the new cap cked out to be right on at 12.5 uf ) The motor is wired correctly with Black and white to load. As the Black wire is for high speed. I also oHm checked the motor and results are
Black to white 2 ohms
Black to brown 35 ohms
white to brown 37 ohms

I know this may be considered an Hvac question, but i was hoping to get someone with electrical knowledge to give me a suggestion.
Is this an indication that the motor is going and should be replaced ?
there are no other symptoms like odors etc. other than slow running.
all the other wires for the 3 remaining speeds and capped off.

anyone have any thoughts ?

Thanks for looking.

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Old 04-06-2010, 07:34 AM   #2
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Motor runs slow


1. Check the voltage both with the motor stopped and with the motor running. Did you make any changes to the wiring?

2. Check to see that all the vents and returns are not clogged with dust and you have not closed off too many of them to balance the heat distribution among the rooms.

Aside from that, motors have several windings (or coils) inside. If one has burned out or there is a loose connection inside, the motor can still run but poorly.

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Last edited by AllanJ; 04-06-2010 at 07:37 AM.
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Old 04-06-2010, 11:13 AM   #3
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Motor runs slow


The ohm readings to brown went to the capacitor circuit so disregard those readings.
What makes you think it's not running full speed? Do you have a way to test RPM's? How many wires do you have available to you in the peckerhead and what colors are they? How is speed adjusted, manually or automatically? Can you post a picture of the motor nameplate and the wires in the connection box (peckerhead)? The thermostat drawing would help too.

I can assure you that if the high speed winding was bad, it would not run in high speed. Since we know nothing about this motor and how it is controlled, there is little we can do. More information is in order. Lots more. See the questions above.
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