Furnace Blower Won't Shut Off

All of a sudden my furnace blower runs constantly even though it is set on "auto" at the thermostat. The heat cycles on and off properly (fortunately because it is 19 degrees outside). The furnace is about 10 years old and is gas. I seem to recall there is a wiring option on the motor for it to run constantly but no one has messed with that since it was installed. I would appreciate any ideas on what the problem might be.
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snipped-for-privacy@usa.com wrote:

sounds like a stuck relay on the control board, try powering it down, tapping on all the relays, and powering back up.
nate
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It could have a relay with a slightly welded contact. Tapping on the furnace or the relay itself could jar it loose.
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Could be a sticking relay, could be a bad thermostat from the heat exchanger. Try turning off all power to the heater and then turn it back on and see if the blower stops when power is restored.
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On Dec 6, 12:49 pm, snipped-for-privacy@usa.com wrote:

First off, disconnect all the wires at the T-stat and see if it shuts off. If it does, you have a faulty t-stat/wiring. If it stays on, put the wiring back for the T-stat, and now disconnect the T-stat wiring at the furnace board to confirm its not the wire shorted in the walls someplace. If it still stays on, it could be a stuck relay on the control board on the furnace. You can try tapping it. Another possibility is that if the chamber/duct temp sensor could be faulty, giving a high reading and could be telling the blower to stay on.
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Thanks everyone!! I appreciate the prompt replies. I powered it down, tapped on everything and it works fine now. Ed S.
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snipped-for-privacy@usa.com wrote:

Good to hear it. However, as I'm sure you know, things that are "fixed" by percussive diagnostics don't always stay fixed, so you may wish to find which relay it is that controls the fan and purchase a replacement. It's likely soldered onto the board so try Digi-Key or a *good* electronics supply.
The contacts may have welded due to excessive current draw by the fan motor, in which case a replacement relay may only last a year or two before failing again. You may want to check it with an ammeter against the rating on the label, and replace the blower if indicated.
Of course, this is best done in the spring, when you're not using heat or A/C :)
nate
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Just power down, and tap on it three times a day for the rest of your life. Very simple.
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Mikepier wrote:

Things that go away by themselves when tapped usually come back by themselves shortly thereafter. <G>
Jeff
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snipped-for-privacy@usa.com wrote:

Hi, First unhook wire on G terminal on your 'stat. If it stops problem is in the ;stst. If not problem is in the furnace, control board of replay depending on how old the furnace is.
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You are fortunate that the unit continued to function. There are several brands that go to continuous fan run to tell you that something needs attention. Most recent units have an electronic control board. There should be a standard "flash" chart on the inside of the blower cover that has the wiring diagram. Count the number of flashes on the board - the chart would tell you what to trouble shoot. There is a daisy chain of safety relays usually with the same color wire looping them together. There is a small reset button on each of these. There is also a limit switch on the burner box and a switch if the power venter doesn't come on.
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responding to http://www.homeownershub.com/maintenance/furnace-blower-won-t-shut-off-346492-.htm moshei wrote:
This gem is located behind the front decorate cover. Remove it and look for a metal box attached to the furnace. It will have a cover on it and the cover will be held in place by two screws.
------------------------------------- TeleTemp Cooling & Heating
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responding to http://www.homeownershub.com/maintenance/furnace-blower-won-t-shut-off-346492-.htm moshei wrote: The gem located behind the front decorate cover. Remove it and look for a metal box attached to the furnace. It will have a cover on it and the cover will be held in tow place by the screws.
------------------------------------- TeleTemp Cooling & Heating
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