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.
On Dec 6, 12:49 pm, firstname.lastname@example.org 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
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*
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 :)
replace "roosters" with "cox" to reply.
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.
Keep the whole world singing . . . .
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