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Blower motor will not come on, there is a hum in the fan limit switch when the blower is turned on

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This is either the motor itself or a capacitor. To check the motor use an amp meter. Clamp the meter around each power lead seperatly try to cycle the motor and verify the reading on the meter. After you have done this check the LRA (locked rotor amps) rating on the motor I.D. tag. If the readings you saw are near or higher than those listed on the motor tag then the motor is bad. Feel free to comment me if you need any other assistence.

Thanks

Posted on Aug 28, 2008

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How do I wire a induce fan motor


Induced fan motors on older units are wired through the high limit safety on the stack - in series. When the furnace calls for heat, the induced fan motor comes on and after a time the furnace will light.

Older units have a temp switch in the stack that rotates to bring on the burners and blower motor. . When there is a call for heat, the induced draft fan motor comes on and then the burners will light.

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Does the fan come on when you turn the Fan to ON at the thermostate? If it does then it could be the blower board not turning the low speed blower tap on. Or the Fan & Limit switch not working. If the fan doesn't come on in the on position then the blower motor could be out or the run capacitor.
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Cleaning the flame sensor has nothing to do with blower motor not turning on. You either one of the following problems 1 bad cap for motor. 2 bad motor. 3 bad limit on blower housing or 4 a bad board. You will need a volt meter to check for these problems. Try seeing if the fans runs with unit of and fan switch turned to on. Also does motor hummmm. Is motor cage free ( can check by manually turning) If motor doesnt humm and the cage is free wheeling then you will need to find out if you have power going to the motor. If you find out that you do then you will need to change blower motor. If you do not have power then you will need to check limit with continuity tester on volt meter. If that checks fine only 1 thing can be wrong and that is the board.

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Push in on the door safety switch,and use a screwdriver to help start the fan motor, while it calling for fan-on, if it takeoff and run , youll probably need to changeout the fan motor & capicator!

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