Breaker flipped when furnace or fan turned on

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Old 04-30-10, 07:42 AM
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Unhappy Breaker flipped when furnace or fan turned on

Whenever I turn on the furnace or the fan through the thermostat, I can hear the fan is on, then immediately a single breaker is tripped, the fan is back to silent and the thermostat lost power. After I flip back that breaker, I can use the thermostat to control again, but as long as I turn on the furnace or the fan, the same breaker is tripped again.

I am not sure what this breaker controls (to the thermostat?) but I am sure it is not the double breaker for the furnace, not the other double breaker for the AC. I can't turn on AC to test through the thermostat, I am not sure if the room temperature is too low, or if the AC is broken.

There is no gas for the property, both furnace and AC are electric.

Thanks!
 
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Old 04-30-10, 07:50 AM
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Since the breaker trips when you turn on the fan only the breaker is the circuit for the furnace. The A/C unit outside is on another circuit. The thermostat gets its power from the furnace itself and is low voltage. Sounds like you are having an issue with your fan motor as it is drawing too much current and tripping the breaker.
 
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Old 04-30-10, 08:24 AM
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Originally Posted by Tolyn Ironhand View Post
Since the breaker trips when you turn on the fan only the breaker is the circuit for the furnace. The A/C unit outside is on another circuit. The thermostat gets its power from the furnace itself and is low voltage. Sounds like you are having an issue with your fan motor as it is drawing too much current and tripping the breaker.
Thanks - is there some thing I can do to make sure that the motor is the problem, before I take it down and replace it with a new one?

By the way, could you point me to a web page with the circuit diagram for the furnace, the fan and the thermostat? I search the web but can't find one. What I found is only the wiring for the thermostat itself, not the diagram among these items. Thanks!
 
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Old 04-30-10, 09:33 AM
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Many cases there is a wiring diagram on the inside cover of the furnace. Otherwise post the manufacture name and number an somebody might be able to find one.

As far as testing the motor, see if you can spin the fan freely. If not then the bearings are shot. Or you can ohm it out with a meter to see if there is a short.

How old is the unit?
 
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Old 04-30-10, 09:52 AM
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Originally Posted by Tolyn Ironhand View Post
Many cases there is a wiring diagram on the inside cover of the furnace. Otherwise post the manufacture name and number an somebody might be able to find one.

As far as testing the motor, see if you can spin the fan freely. If not then the bearings are shot. Or you can ohm it out with a meter to see if there is a short.

How old is the unit?
Thanks - I will test the spinning and test if there is a short. By the way, a while ago when I was working with a friend on his furnace, there is a capacitor somewhat on his fan motor. Is there something I might check my capacitor? Or if the short test you mention takes care of it?

Regarding to the age of the furnace, the property was build in 1974. I think that is the age of the furnace. Thanks!
 
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Old 05-01-10, 07:36 PM
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Originally Posted by Tolyn Ironhand View Post
Many cases there is a wiring diagram on the inside cover of the furnace. Otherwise post the manufacture name and number an somebody might be able to find one.

As far as testing the motor, see if you can spin the fan freely. If not then the bearings are shot. Or you can ohm it out with a meter to see if there is a short.

How old is the unit?
I think you are right - motor is the cause of the problem. Although it can spin freely but I disconnected it and found that there is virtually a short. After disconnecting the motor, the lines to to motor have a 110 volt as expected, and the other part "sounds" working. But after re-connecting the motor, a spark and a breaker tripping would happen immediately.

I will replace a new motor and hoping the problem will go away. One more question, I can't find a capacity next to the motor. Is it possible that there is no capacity, or if only I did not find it?

Thanks!
 
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Old 05-24-10, 10:38 AM
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Tolyn,

You are absolutely right about the motor! After I replaced with a new motor, everything works fine. Please don't blame me about replying so late, because I only actually fixed it yesterday. I have one trip to the store with the moter/fan assembly, three trips to the store for three kinds of puller (trying to remove the motor from the fan brades assembly), one trip to the store to get a tremel to cut the hud so the puller can fit in; three trips to different stores that don't have this kind of motor, and SIX trips to Grainger which has the motor! The 1st trip to place an order (I showed them the old motor); the 2nd trip to bring the new motor home and found it has a different diameter; 3rd trip to take it back to the store and they said they could ordered me a new support-legs to fit; 4th trip to found out that support-legs didn't fit and they said this time they found the matched motor; 5th trip to found out the warehouse sent them the wrong one; and finally the 6th trip to get the new and right one home!

Am I the poorest DoItYourSelf guy?

Thanks!
One question, I ohm'ed both old and new motor and found both of them have no resistance. I think the new one will when the AC applies to it.
 
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