Question about a gas furnace blower motor

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Old 12-30-09, 07:23 PM
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Question about a gas furnace blower motor

We have an older GE gas furnace and just replaced the blower motor. The old motor was a 3 speed. The new motor is a 4 speed energy efficient model.

The furnace is functioning, but the motor will come on for about 30 seconds, then it shuts off for the same amount of time and comes back on. The burners are not going out.

Can anyone tell me why it is doing this? Is this normal? If not, what could be causing this to happen?

Thanks in advance for any help.
 
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Old 12-30-09, 11:34 PM
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Is the motor hot to the touch? If so, it might be shutting off on the motor temperature limit switch.

If not, I'd use a multimeter to determine whether the 120 VAC power to the motor stays on when the motor shuts, off, or if the power is being shut off by the fan switch or circuit board.
 
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Old 12-31-09, 06:05 AM
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Thanks for your reply.

The motor isn't running hot. I guess that means we need a new circuit board. The cheapest one I could find was $370. Do you know if we have to use an OEM part or if there are compatible circuit boards by other manufacturers? It seems the GE models are the priciest.

Thanks again.
 
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Old 12-31-09, 07:10 PM
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The blower fan might be going out according to the a heat controlled fanswitch setting. And/or if your house is too cold, the cold return air drops the heat exchanger temp and shuts off the fan.
 
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Old 12-31-09, 07:43 PM
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I'd check to verify that you have 120 VAC
 
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Old 12-31-09, 07:46 PM
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In my view it's a mistake to guess that you need expensive new parts. Check to see if you have 120 VAC to the motor.

You might have the new motor improperly wired, or there could be other problems.

If you don't know how to identify where the problem is, the smart solution is to have a pro diagnose the problem for you.

Why was the fan motor changed out, and who did it?
 
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Old 01-02-10, 04:59 AM
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Thanks for your replies.

The blower motor burned out (on Christmas Eve, no less, with wind chill temps of -10).

It was switched out by my brother in law who is an electrician. The wiring is correct (it is getting 120 VAC) and the motor is functioning well (the house is maintaining the temperature set on the thermostat and it's running much quieter), it's just that we're used to the furnace coming on and running longer. With this new motor, it comes on, goes off, comes on, goes off.
 
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Old 01-02-10, 05:31 AM
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Originally Posted by LarkBea View Post
With this new motor, it comes on, goes off, comes on, goes off.
The burner stays on the whole time, and the fan motor stops and go?

Either the fan speed is set too high, or the fan limit control is set too low.
 
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Old 01-02-10, 06:17 AM
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Originally Posted by LarkBea View Post
It was switched out by my brother in law who is an electrician. The wiring is correct (it is getting 120 VAC) and the motor is functioning well (the house is maintaining the temperature set on the thermostat and it's running much quieter), it's just that we're used to the furnace coming on and running longer. With this new motor, it comes on, goes off, comes on, goes off.
When you say it is getting 120VAC, what do you mean? Is it getting 120 VAC when the motor is off? If so, you have a problem.

You should also check the limit switch to determine whether the furnace is overheating and the limit switch is shutting the burners off.

Do you have a meter that allows you to measure 24 VAC and 120 VAC and understand how to use it?
 
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Old 01-02-10, 09:46 AM
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The burner stays on the whole time, and the fan motor stops and go? Correct.

When you say it is getting 120VAC, what do you mean? Is it getting 120 VAC when the motor is off?
No. It is getting 120VAC when the motor is running.

Do you have a meter that allows you to measure 24 VAC and 120 VAC and understand how to use it? My brother in law does and I'm sure he knows how to use it. Me? No. I tend to hide under the bed when anything electrical goes haywire. Cars, too.

Thanks for your replies. I'm saving everything and emailing my brother in law.
 
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Old 01-02-10, 11:08 AM
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Originally Posted by LarkBea View Post
When you say it is getting 120VAC, what do you mean? Is it getting 120 VAC when the motor is off?[/I] No. It is getting 120VAC when the motor is running.

It's a safe bet that the motor is getting 120 VAC when it running, but there are reasons it could shut off when it still has 120VAC to it. The problem would be different than if the motor is stopping because the 120VAC has been shut off.

Since you don't have a voltmeter, you probably don't know at this point, but it's one of the things your BIL can check when he makes an appearance.
 
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Old 01-02-10, 11:47 AM
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Since you don't have a meter, check the fan limit control, and wach the dial.. If the fail is moving all the time, then let us know waht the tabs are set to.

There should be 3 tabs.

-on
-off
-limit
 
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Old 01-05-10, 04:52 PM
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High speed blower wire is likely hooked up to HEAT connection, causing a temp drop in the heat exchanger when the blower comes on, turning off blower prematurely, as the switch rotates to the OFF position, rather than climbing in temp, and then remaining steady thereafter.

Solution: Hook up the correct blower speed wire to the control. Also per Jay, the fan limit settings may not be quite right, and may be set too close between the OFF and ON settings. The order on a Honeywell switch, to be clear, is actually first OFF, then ON, then LIMIT, when read in order of it's operational rotation.
 
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