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Old 03-31-2011, 11:14 AM   #1
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Induction motor and thermostat


I replaced the induction motor about 1 1/2 years ago. When the thermostat is in the off position, the induction motor runs. If I cut off power to furnace, turn thermostat on, and then turn power back on to the furnace, the induction motor runs even if the termostat is set well below current temperature. Is the thermostat bad?

Thanks in advance.

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Old 03-31-2011, 12:52 PM   #2
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Induction motor and thermostat


There needs to be a few step taken to find out.
1st remove the low voltage wire at the furnace.
If the motor stops then the 2 problems could be thermostat or the thermostat wire could have a short.
2nd if motor still runs after the low voltage wires are removed than there is a problem with control board for furnace.
Good Luck.

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Old 03-31-2011, 01:31 PM   #3
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Induction motor and thermostat


How can I identify the low voltage wire you are referring to?
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Old 03-31-2011, 01:38 PM   #4
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Induction motor and thermostat


There are line voltage wires, the ones that power off the system, shut that off 1st.
The low voltage wires are usually in a brown or wire.
They will be going into the base of the furnace and will usually have 3 to 5 wires together they have a color coating that you must mark and replace in the same spot that you removed them from.
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Old 04-01-2011, 08:09 AM   #5
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Induction motor and thermostat


If the inducer motor is the only thing that runs, then the control board is probably the culprit. If the furnace also starts the fire and then starts the blower motor, to heat the house as it normally would, then it could be the t/stat, t/stat wiring, or the control board.
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Old 04-28-2011, 10:26 AM   #6
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Induction motor and thermostat


I'm not finding the wiring you are describing. I have a Janitrol furnace, manufactured by Goodman. The model is GPD125-4 9904602630.
Would it be possible to determine exactly what I should see and tell me? I'm a pastor and trying to save our church some money.
Thanks in advance.
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Old 04-28-2011, 05:55 PM   #7
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Induction motor and thermostat


On the circuit board there are several small black plastic relays approx 1/2"x1/2". One of them is for the inducer fan motor. Try carefully tapping them with a screwdriver. If the fan stops then the relay and board are faulty.
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Old 05-03-2011, 10:18 AM   #8
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Induction motor and thermostat


I just noticed that when I turn the power on to the furnace, the circuit board is blinking a code that indicates there is an "open limit switch." It says to check the main limit switch or the aux. limit switch. Any help with that?
Thanks
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Old 05-03-2011, 04:24 PM   #9
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Induction motor and thermostat


The limit switch and I am not familiar with that exact model sits above the burners and has 2 wires to it. If it is blown you really should get a Pro/tech out to find out why it is blown. Heat rise test etc needs to be done.
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Old 05-03-2011, 10:02 PM   #10
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Induction motor and thermostat


Quote:
Originally Posted by dklank View Post
I just noticed that when I turn the power on to the furnace, the circuit board is blinking a code that indicates there is an "open limit switch." It says to check the main limit switch or the aux. limit switch. Any help with that?
Thanks

You just diagnosed it. Either a wire has broken/fallen off or one of those siwtches have failed.

There is a diagnostic/repair technique called the "wire jiggle test" which involves carefully moving some of the suspect wiring. If you are lucky, you will see a wire that is hangiing loose or has broken 99% of the way through.

It should be noted, as mentioned by others here, that a gas furnace has the very real capacity of killing somebody, so a service call would be the most sensible approach.

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