Furnace Blower Motor Control ...

[zzzzzzz]

My home "forced air" gas furnace has a mechanical device composed of a "sprial bi-metal" and "electrical contacts" that turn on and off the furnace blower motor based on internal furnace air temperature. It is mounted on the front of the "hot air chamber". This "blower control" can be adjusted by moving two external "tabs" to trigger the the "on" and "off" sequence at different temperature settings. My problem is the "adjustment" between the blower not shutting off at all and shutting off to soon .. causing several "30 second" on-off cycles" .. is 1/8 of an inch. I think its time for a replacement.

Instead of putting in another "bi-metal mechanical device" is there a "solid state/electronic" blower control that is easier to adjust and more linear in response.

Thanks in advance.

[htg guy]

Furnaces that were built with the insertion type of fan/limit control will very rarely work with any other type of control. Once they are set to the desired temperature, there is never a reason to adjust them. If your furnace is cycling, there may be other problems with it that need to be addressed. These controls can wear out or fail and need to be replaced with the same style, and with the same length insertion tube.

For your safety; instead of just replacing the fan/limit, I would have a heating contractor take a look at the entire furnace to ensure that it did simply fail, and that its failure was'nt due to some other problem.

[plain spoken]

Originally posted by zzzzzzz
My home "forced air" gas furnace has a mechanical device composed of a "sprial bi-metal" and "electrical contacts" that turn on and off the furnace blower motor based on internal furnace air temperature. It is mounted on the front of the "hot air chamber". This "blower control" can be adjusted by moving two external "tabs" to trigger the the "on" and "off" sequence at different temperature settings. My problem is the "adjustment" between the blower not shutting off at all and shutting off to soon .. causing several "30 second" on-off cycles" .. is 1/8 of an inch. I think its time for a replacement.

Instead of putting in another "bi-metal mechanical device" is there a "solid state/electronic" blower control that is easier to adjust and more linear in response.

Thanks in advance.

Not meaning to be a pain here, but how does someone with so little knowledge of the business become a "Professional Member" ?

[41gasman]

Plain Spoken:
Becaaaause I be saying I are ones.
Duuuua!!!

Also from the fornases me
bot in the intornett place.
THEY say things be like
dryer vent looking filters?
Filters?
And broken down fire exchagers.

Buba the Jeteye master.
Ruler of ALL thats in my mind!

[docholiday]

Odds are someone already replaced it once and used a different insertion length. If not, then you better take a look at the airflow, there was never anything wrong with the control you speak of other than too many people can monkey around with it.

[coolwhip]

Originally posted by plain spoken

Originally posted by zzzzzzz
My home "forced air" gas furnace has a mechanical device composed of a "sprial bi-metal" and "electrical contacts" that turn on and off the furnace blower motor based on internal furnace air temperature. It is mounted on the front of the "hot air chamber". This "blower control" can be adjusted by moving two external "tabs" to trigger the the "on" and "off" sequence at different temperature settings. My problem is the "adjustment" between the blower not shutting off at all and shutting off to soon .. causing several "30 second" on-off cycles" .. is 1/8 of an inch. I think its time for a replacement.

Instead of putting in another "bi-metal mechanical device" is there a "solid state/electronic" blower control that is easier to adjust and more linear in response.

Thanks in advance.

Not meaning to be a pain here, but how does someone with so little knowledge of the business become a "Professional Member" ?

Excellent question!!!

[Swampfox]

The "professional member" status is automatic to whoever signs up due to the number of people who applied, definately not a good policy but we should report anyone who shouldnt be one, such as this DIY'er

Originally posted by BC1
Because of the sheer number of "Professional Members," we are leaning towards a system where everyone who applies will be admitted automatically. However, if there are requests for removal of a Pro Member by others, we may launch an investigation of sorts. It's kind of an honor system and allows the initial screening process to be conducted by your peers.

[Edited by swampfox on 01-30-2005 at 10:29 PM]

[sctech]

maybe its martha stuart working on the big house's furnace

[41gasman]

So does this mean ANYONE can go into
the business and marketing forum.
If so whats the point?

[Swampfox]

It means they can get in at first, its our job to point out the ones that dont belong, but what if they never post and just lurk, like I said not a good policy.

[coolwhip]

So Zzzzzz, where is your input on this? and BC, where is your input on this?

[rimek]

Maybe he's trying to get the right "terms" to respond, when he should be using the "telephone" to call a qualified "technician."

[zzzzzzz]

I'm back .. your all right. As for signing up as a professional member I justified it based on "I work for Siemens, USA" as an engineer. My division of Siemens is a "2nd tier" supplier of solid state "micro" electronics, such as power supplies, switching elements and sensing controls for "1st tier" manufactures of some HVAC components (among other devices) to the world market.

Didn't mean to demeam anyone's status or inpersonate an experienced HVAC professional (as if I could). I came here with an open mind seeking information. Can I contribute to this site .. I believe so.

Thanks to all who addressed my problem. Yes, the fan limit control was replaced about 4 years ago by a local HVAC company, as related by the prior home owner, and it fixed the same problem then that I'm having now.

So, if I understood correctly, there is no new, state-of-the-art replacement for the old reliable fan limit switch which will only "stop working completely" but not "wear out slowly". I will check to see if my "Ruud" furnace has the proper bi-metal sensor length as suggested.

Any other additional info or suggestions will be appreciated. Thanks.

[casturbo]

I'd make sure the exact type and length of fan control was installed on the furnace when it was replaced. These controls are critical to heat exchanger longevity. Just a minor adjustment to these controls can wreak havoc on x-changer temperature.

[htg guy]

Originally posted by htg guy
These controls can wear out or fail and need to be replaced with the same style, and with the same length insertion tube.

For your safety; instead of just replacing the fan/limit, I would have a heating contractor take a look at the entire furnace to ensure that it did simply fail, and that its failure was'nt due to some other problem.

I can't find a comment from anybody telling you that these controls "stop working completely" but "not wear out slowly".

You have a problem that needs to be addressed. Its not normal for fan/limit controls to wear out every four years. Call someone and have them check over the furnace.

[zzzzzzz]

"casturbo" and "htg guy" ...

Thank you both for the advice which I will follow.