furnace blower sticks on

Posted by Mikepier on November 6, 2009, 8:55 am

> So really I either need to replace it or file the contacts. =A0I'd like
> to try the filing, but can anyone tell me where the contacts are? =A0If
> I do need to replace it, can anyone tell me if it's a straighforward
> replacement job?
> Thanks

It is straightfoward. All it is is just a probe sticking into the
plenum, and the unit is held by 2 screws. Plus you have to remove the
wiring, so make sure the power is off.
The only thing you have to check is the length of the probe, they make
some with 5", 8" or 11.5". Get the model # off the inside of the cover
case. If your not in a rush and if the weather cooperates, you can get
one online for cheaper in a few days.

Posted by DerbyDad03 on November 6, 2009, 9:16 am

> > I'm with some of the other posters here... I think the control is misad=

justed. =A0That little metal

> > tab sticking out near the "50" marking controls when the fan turns on a=

nd off, and can be moved. =A050

> > is way too low a setting, it should be closer to 100. =A0The "Off On" m=

arkings under the word "Fan"

> > indicate the range where that is supposed to be.
> > Eric Law

> Okay, sorry I should have clarified before. =A0I took the pic at a point
> where I was experimenting with the adjustments. =A0The metal tabs are
> usually set around 130 (high) and 80 (low). =A0I had pushed the lower
> one down to 50 so that I could slowly move it up and see at which
> point the blower shut off. =A0The problem is that when it does stick, it
> requires only the slightest touch to un-stick - so it's impossible to
> hold the dial and move the tab without manually "unsticking" it. =A0The
> issue is definitely not the setting, since when I have it set on 80,
> the blower continues to run until I manually unstick it - at one point
> i was out of town and my wife said it ran for 2 days straight, and
> upon coming home and measuring the temp of the air in the plenum, it
> was much lower than 80.
> So really I either need to replace it or file the contacts. =A0I'd like
> to try the filing, but can anyone tell me where the contacts are? =A0If
> I do need to replace it, can anyone tell me if it's a straighforward
> replacement job?
> Thanks

Do you have a humidifier attached to the furnace?

My old furnace had a humidifer and the probe-type fan limit switch
described in this thread.

When I had a problem with my blower staying on/not coming on, I pulled
the fan-limit probe and found it coated in mineral deposits - that
white flakey stuff.

I replaced the limit switch and yanked the humidifier and all was well.

Posted by hr(bob) hofmann@att.net on November 6, 2009, 3:41 pm

> > > I'm with some of the other posters here... I think the control is mis=

adjusted. =A0That little metal

> > > tab sticking out near the "50" marking controls when the fan turns on=

and off, and can be moved. =A050

> > > is way too low a setting, it should be closer to 100. =A0The "Off On"=

markings under the word "Fan"

> > > indicate the range where that is supposed to be.
> > > Eric Law

> > Okay, sorry I should have clarified before. =A0I took the pic at a poin=

> > where I was experimenting with the adjustments. =A0The metal tabs are
> > usually set around 130 (high) and 80 (low). =A0I had pushed the lower
> > one down to 50 so that I could slowly move it up and see at which
> > point the blower shut off. =A0The problem is that when it does stick, i=

> > requires only the slightest touch to un-stick - so it's impossible to
> > hold the dial and move the tab without manually "unsticking" it. =A0The
> > issue is definitely not the setting, since when I have it set on 80,
> > the blower continues to run until I manually unstick it - at one point
> > i was out of town and my wife said it ran for 2 days straight, and
> > upon coming home and measuring the temp of the air in the plenum, it
> > was much lower than 80.
> > So really I either need to replace it or file the contacts. =A0I'd like
> > to try the filing, but can anyone tell me where the contacts are? =A0If
> > I do need to replace it, can anyone tell me if it's a straighforward
> > replacement job?
> > Thanks

> Do you have a humidifier attached to the furnace?
> My old furnace had a humidifer and the probe-type fan limit switch
> described in this thread.
> When I had a problem with my blower staying on/not coming on, I pulled
> the fan-limit probe and found it coated in mineral deposits - that
> white flakey stuff.
> I replaced the limit switch and yanked the humidifier and all was well.- =

Hide quoted text -

> - Show quoted text -

When I described filing the contacts, I should have said replacing the
limit switch was a good option if you can get a replacement with
similar mounting holes and probe size. The humidifier dust collecting
is logical, altho I have never heard of it being a problem before.

Posted by DerbyDad03 on November 6, 2009, 3:55 pm

wrote:

> > > > I'm with some of the other posters here... I think the control is m=

isadjusted. =A0That little metal

> > > > tab sticking out near the "50" marking controls when the fan turns =

on and off, and can be moved. =A050

> > > > is way too low a setting, it should be closer to 100. =A0The "Off O=

n" markings under the word "Fan"

> > > > indicate the range where that is supposed to be.
> > > > Eric Law
> > > Okay, sorry I should have clarified before. =A0I took the pic at a po=

int

> > > where I was experimenting with the adjustments. =A0The metal tabs are
> > > usually set around 130 (high) and 80 (low). =A0I had pushed the lower
> > > one down to 50 so that I could slowly move it up and see at which
> > > point the blower shut off. =A0The problem is that when it does stick,=

> > > requires only the slightest touch to un-stick - so it's impossible to
> > > hold the dial and move the tab without manually "unsticking" it. =A0T=

> > > issue is definitely not the setting, since when I have it set on 80,
> > > the blower continues to run until I manually unstick it - at one poin=

> > > i was out of town and my wife said it ran for 2 days straight, and
> > > upon coming home and measuring the temp of the air in the plenum, it
> > > was much lower than 80.
> > > So really I either need to replace it or file the contacts. =A0I'd li=

> > > to try the filing, but can anyone tell me where the contacts are? =A0=

> > > I do need to replace it, can anyone tell me if it's a straighforward
> > > replacement job?
> > > Thanks

> > Do you have a humidifier attached to the furnace?
> > My old furnace had a humidifer and the probe-type fan limit switch
> > described in this thread.
> > When I had a problem with my blower staying on/not coming on, I pulled
> > the fan-limit probe and found it coated in mineral deposits - that
> > white flakey stuff.
> > I replaced the limit switch and yanked the humidifier and all was well.=

- Hide quoted text -

> > - Show quoted text -

> When I described filing the contacts, I should have said replacing the
> limit switch was a good option if you can get a replacement with
> similar mounting holes and probe size. =A0The humidifier dust collecting
> is logical, altho I have never heard of it being a problem before.- Hide =

quoted text -

> - Show quoted text -

re: dust collecting

Trust me, it was not dust.

The probe was caked with minerals deposits from our hard water.

I did replace the entire fan-limit switch (White-Westinghouse)
although the replacement was not an exact match so I had to adapt the
mounting location a bit.

The biggest problem was that the exterior housing was much smaller and
it was really tough to get the wiring inside the housing and clip the
cover back on.

Posted by Lefty on November 7, 2009, 6:21 am

> I'm with some of the other posters here... I think the control is
> misadjusted. That little metal
> tab sticking out near the "50" marking controls when the fan turns on and
> off, and can be moved. 50
> is way too low a setting, it should be closer to 100. The "Off On"
> markings under the word "Fan"
> indicate the range where that is supposed to be.
> Eric Law

Okay, sorry I should have clarified before. I took the pic at a point
where I was experimenting with the adjustments. The metal tabs are
usually set around 130 (high) and 80 (low). I had pushed the lower
one down to 50 so that I could slowly move it up and see at which
point the blower shut off. The problem is that when it does stick, it
requires only the slightest touch to un-stick - so it's impossible to
hold the dial and move the tab without manually "unsticking" it. The
issue is definitely not the setting, since when I have it set on 80,
the blower continues to run until I manually unstick it - at one point
i was out of town and my wife said it ran for 2 days straight, and
upon coming home and measuring the temp of the air in the plenum, it
was much lower than 80.

So really I either need to replace it or file the contacts. I'd like
to try the filing, but can anyone tell me where the contacts are? If
I do need to replace it, can anyone tell me if it's a straighforward
replacement job?

Thank

Just change it out Matt.
Those exact models sticking with age is very, very common. It's super easy
to replace. You just need a nutdriver to remove it, and a small regular
screwdriver to release the wires. Two things to remember 1.) Put those
wires in the exact same place!!! Your furnace may have both 24 volts and
120volts going through that switch at the same time since it is both a fan
and limit switch, so you don't want to fry anything. 2.) On the new unit,
there will likely be a jumper between the two bottom terminals. This was
for three wire set-ups, and would make the switch all 120volt. You have a
four wire set-up, so you will want to remove it. There are three different
lengths available, and also some have a internal heater to bring the fan on
sooner. It is'nt really going to make a lot of difference which one you
use, any of the Honeywell L4064 fan/limits will work essentially the same in
your older furnace, and you probably could'nt tell the difference which one
you had used unless you're the kind of guy who times the blower with a
stopwatch. There are also other fan limits available, but it would be way
simpler for you to find an L4064. Don't forget to set the dial pins at the
temps that the furnace manufacutrer recommended.

HTH, Lefty

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furnace blower sticks on - Page 3