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Heat Overload turns on Furnace Blower

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Heat Overload turns on Furnace Blower maradcliff 07-15-2005
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Posted by on July 15, 2005, 11:51 pm


We have been having a heat wave, with temps up near 100 degrees for
well over a week. Today it got so hot in my house that the furnace
blower kicked on. I thought that was rather odd, since I do not have
central AC. Then it hit me. It was so friggin hot that the furnace
sensor (probably a klixon) thought the burner was on, and the blower
kicked in. I shut off the power to the furnace, but that tells me
it's time to set up my tent, since it's just too frikkin hot to stay
in the house, especially since Sunday is supposed to hit some sort of
heat record.

Mark


Posted by on July 16, 2005, 4:58 am


Good to hear it's happened to you too.
I've been watching a friends house while he's away.

The thermostat has <HEAT> <OFF> <COOL> setttings,
and it was set to <OFF>

THe inside of the house was close to 100 degrees,
and the furnace blower motor was running.

The only way I could get it to stop was to
flip the circuit breaker !

I was getting ready to call a HVAC guy until I read your post.



On Fri, 15 Jul 2005 23:51:04 -0500, maradcliff@UNLISTED.com wrote:

>We have been having a heat wave, with temps up near 100 degrees for
>well over a week. Today it got so hot in my house that the furnace
>blower kicked on. I thought that was rather odd, since I do not have
>central AC. Then it hit me. It was so friggin hot that the furnace
>sensor (probably a klixon) thought the burner was on, and the blower
>kicked in. I shut off the power to the furnace, but that tells me
>it's time to set up my tent, since it's just too frikkin hot to stay
>in the house, especially since Sunday is supposed to hit some sort of
>heat record.
>
>Mark

<rj>


Posted by Steve@carolinabreezehvac.com on July 16, 2005, 8:06 am



> Good to hear it's happened to you too.
> I've been watching a friends house while he's away.
>
> The thermostat has <HEAT> <OFF> <COOL> setttings,
> and it was set to <OFF>
>
> THe inside of the house was close to 100 degrees,
> and the furnace blower motor was running.
>
> The only way I could get it to stop was to
> flip the circuit breaker !
>
> I was getting ready to call a HVAC guy until I read your post.


If its an older model, with a bi-metal adjustable fan limit switch, its
either set too low, or out of calibration..
the overload is normally set at 250F..so..guess what?

>
>
>
> On Fri, 15 Jul 2005 23:51:04 -0500, maradcliff@UNLISTED.com wrote:
>
> >We have been having a heat wave, with temps up near 100 degrees for
> >well over a week. Today it got so hot in my house that the furnace
> >blower kicked on. I thought that was rather odd, since I do not have
> >central AC. Then it hit me. It was so friggin hot that the furnace
> >sensor (probably a klixon) thought the burner was on, and the blower
> >kicked in. I shut off the power to the furnace, but that tells me
> >it's time to set up my tent, since it's just too frikkin hot to stay
> >in the house, especially since Sunday is supposed to hit some sort of
> >heat record.
> >
> >Mark
>
> <rj>



Posted by lp13-30 on July 16, 2005, 9:42 am


If that furnace is in the attic it is possible for the temperature to
get high enough occasionally for a bi-metal fan switch to to close even
if it is properly adjusted. I have also seen it happen on mobile homes
with the fixed disc fan switches. Solution-- run the A/C. Larry



Posted by Mark on July 17, 2005, 7:35 am




Steve@carolinabreezehvac.com wrote:
> > Good to hear it's happened to you too.
> > I've been watching a friends house while he's away.
> >
> > The thermostat has <HEAT> <OFF> <COOL> setttings,
> > and it was set to <OFF>
> >
> > THe inside of the house was close to 100 degrees,
> > and the furnace blower motor was running.
> >
> > The only way I could get it to stop was to
> > flip the circuit breaker !
> >
> > I was getting ready to call a HVAC guy until I read your post.
>
>
> If its an older model, with a bi-metal adjustable fan limit switch, its
> either set too low, or out of calibration..
> the overload is normally set at 250F..so..guess what?
>
> >

Well its not just the overheat setting

My furnace blower continues to run after the fire shuts off as the heat
exchanger cools down and it continues to run untill the air is at about
100 F. Due to hystereisis it takes a higher temp to get it to turn
on, but onece on, it won't turn off untill the air drops below 100F.

His blower control may be a bit out of adjustment but not anything
serious.

Mark



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