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Old 10-16-2011, 03:31 PM   #16
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Furnace continues to run after system shuts down


Locate it, and put a jumper across it.

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Old 10-20-2011, 10:26 AM   #17
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Furnace continues to run after system shuts down


The new computer board came today. I installed it but left the thermostat wires off for a quick test. It is still doing the same thing with the new board.
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Old 10-20-2011, 03:09 PM   #18
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Furnace continues to run after system shuts down


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While it could be the board. Don't be surprised if the new board does the same thing.
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Bypass the high limit and see if it does it. Check boar for burnt resister.
Did you check the high limit yet?
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Old 10-20-2011, 03:16 PM   #19
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Furnace continues to run after system shuts down


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Did you check the high limit yet?

I can't find it. All I see in there is:

Blower
A capacitor connected to the blower
Fan board (just replaced)
A Transformer next to the board with 4 wires, two on the top and 2 on the bottom.
3 black relays with what looks like 4 wires each, all the way in the back

I took a photo of this on the blower which shows everything I see in there:

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Old 10-20-2011, 03:19 PM   #20
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Furnace continues to run after system shuts down


Post pic of relays. And of heater area.
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Old 10-20-2011, 03:43 PM   #21
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Furnace continues to run after system shuts down


Here is a picture of the blower:



And this is the board and just behind the board you can see the transformer:



This is the heater area:



And this is the best shot I could get of one of the relays, they are way back there:

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Old 10-20-2011, 09:14 PM   #22
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Furnace continues to run after system shuts down


Try removing one wire from eah relay, and see if that shuts the blower off. Be careful to mark whee the wire came from.
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Old 10-21-2011, 06:05 AM   #23
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Furnace continues to run after system shuts down


Does it matter which wire I remove from the relays?
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Old 10-21-2011, 09:50 AM   #24
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Furnace continues to run after system shuts down


I found the limit switch and the heater! I had to disconnect the two breakers from the wires and the whole tray slides out with the relays attached to it. In the very back behind the relays is the limit switch and hidden behind the tray itself is heater coils.
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Old 10-21-2011, 09:54 AM   #25
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Furnace continues to run after system shuts down


So with nothing powered and everything off my meter says there is continuity between the two prongs on the limit switch. Is that normal or should it be closed right now?
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Old 10-21-2011, 10:42 AM   #26
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Furnace continues to run after system shuts down


I managed to get it out, here is a photo of the whole thing:

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Old 10-21-2011, 10:51 AM   #27
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Furnace continues to run after system shuts down


With my meter set to 200 Ohms, when I my meters two leads are touched together the display reads 00.2.

When I put the leads on the limit switch it reads 00.2. When I press the button on the back of the limit switch it reads 1.

I think this means the limit switch is ok, can anyone confirm this please?
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Old 10-21-2011, 03:26 PM   #28
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Furnace continues to run after system shuts down


The limit is closed and from your readings and appears ok.
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Old 10-21-2011, 03:32 PM   #29
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Furnace continues to run after system shuts down


Could it be one of the 3 relays? How can I test those?
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Old 10-21-2011, 03:44 PM   #30
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Furnace continues to run after system shuts down


See if the contacts are open or closed when they should be open. Use your ohm meter before you put it back in.

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