fan short cycles but it isn't the switch

Posted by njem on November 4, 2006, 6:06 pm

I have a problem with the fan short cycling when the house is cool. The
house may be around 65 and the furnace kicks on and then the fan kicks
on and off in maybe 30 second cycles for maybe 10 minutes and then
finally runs till the house is warm. It does this a little when the
house is warm.

Details:
Interthem gas forced air heat only in a doublewide manufactured house.

This worked fine in its early years and gradually developed this
problem and gradually getting worse.

Had a licensed furnace guy service it and said everything was fine but
maybe the fan switch which he replaced (with a t-o-d60t82 f110-20f).
Couldn't test it then because it was a warm day and it didn't exhibit
the problem.

Called him back and he said to check from the roof for anything
blocking air in or out (a two layer flue pipe). Nothing there.

Flame stays steady and seems to be fine.

I just want to get some input to minimize troubleshooting time with the
furnace guy.

Just for laughs I should switch to electric heaters. With electric at
7cent/kwhr and propane at 2.15 I'd be better off with electric!

Thanks,
Tom

Posted by danger@heat.com on November 4, 2006, 6:23 pm

Well don't let the house drop to 65 degrees. If the fan moves cold
air across the furnace too fast it causes the fan to cycle.
Is there a fan off setting you can lower? Or a fan on setting you
can raise? Did somebody change the blower motor recently? Have the
speeds been changed? Whats changed since last year, or has this
always been a problem?

-Canadian Heat

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Posted by Noon-Air on November 4, 2006, 9:00 pm

> Well don't let the house drop to 65 degrees. If the fan moves cold
> air across the furnace too fast it causes the fan to cycle.
> Is there a fan off setting you can lower? Or a fan on setting you
> can raise? Did somebody change the blower motor recently? Have the
> speeds been changed? Whats changed since last year, or has this
> always been a problem?
> -Canadian Heat

The fan switch on this furnace is a klixon type switch

Posted by Stormin Mormon on November 4, 2006, 6:24 pm

I'd want to watch the dial in the fan limit switch. If the fan is
blowing out all the heat, could be the heat exchanger is cooling and
reheating. Or at leat the fan limit switch is cooling and reheating.

Could also be a motor problem. But, with a regular on and off like
this, I doubt that to be the case.

Don't know from here if you have a three speed fan, might use a lower
speed. I've also heard of a device called a camstat, never used one.
It delays the fan turn on, and then runs the fan continuous until the
end of the call for heat. Or so I remember.

Please let us know how things turn out.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
.

I have a problem with the fan short cycling when the house is cool.
The
house may be around 65 and the furnace kicks on and then the fan kicks
on and off in maybe 30 second cycles for maybe 10 minutes and then
finally runs till the house is warm. It does this a little when the
house is warm.

Details:
Interthem gas forced air heat only in a doublewide manufactured house.

This worked fine in its early years and gradually developed this
problem and gradually getting worse.

Had a licensed furnace guy service it and said everything was fine but
maybe the fan switch which he replaced (with a t-o-d60t82 f110-20f).
Couldn't test it then because it was a warm day and it didn't exhibit
the problem.

Called him back and he said to check from the roof for anything
blocking air in or out (a two layer flue pipe). Nothing there.

Flame stays steady and seems to be fine.

I just want to get some input to minimize troubleshooting time with
the
furnace guy.

Just for laughs I should switch to electric heaters. With electric at
7cent/kwhr and propane at 2.15 I'd be better off with electric!

Thanks,
Tom

Posted by njem on November 4, 2006, 6:46 pm

There are no separate fan on/off settings to adjust. No new motor or
speed change. The fan is one speed. I've always let the house get cool
at night both as a preference and to save gas. When the furnace was
young this wasn't a problem and it very slowly started this problem and
got worse. Now it does it some even when the house is warm.

A handy friend wondered if carbon had built up somewhere. I saw where
the whole panel where the valve/burner goes in could come off so I
looked in there and the burn chamber looks clean to me, except for a
very thin coating of a white chalky substance. Very thin like a too
thin paint job with watery paint. I assume this is just burn residue
and if it's white it must be burning itself off as it goes along?

Thanks,
Tom

Stormin Mormon wrote:

> I'd want to watch the dial in the fan limit switch. If the fan is
> blowing out all the heat, could be the heat exchanger is cooling and

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