AprilAire Humidistat

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I have an AprilAire. It seems that when I turn the humidistat to the point of right where it clicks on, the humidifier runs with each and every furnace cycle. If I turn it until it just clicks off, it never runs with any furnace cycle.
I guess I would expect that setting it right at the brink would make the humidifier run occasionally. But my house goes from either being a desert, to having moss and ferns growing on the walls.
Should it behave like this, or do I need to replace the humidistat? I would be interested in hearing from other AprilAire owners.
I have the model that sits on the cold-air return side. The humidistat is also on the cold-air return duct. Maybe that's part of the problem. Maybe it should be on the hot side.
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Buck Turgidson wrote:

You really need to check the installation manual to determine how that should be set up. On mine the sensor is not a humidity sensor it is a out side temperature sensor that reduces the humidity setting when the temperature outside gets cold to avoid condensation on the windows. Your owners manual should give you some information as well. Yours may be different than mine.
Either way I don't think it should not run unless the indoor humidity is rather high already. You may have a bad wire or connection.
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Joseph Meehan

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Buck Turgidson wrote:

Hi, Maybe the 'stat is located in wrong place? Mine is on the living room wall next to thermostat. Tony Tony
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The unit I got last year is completely different than the one it replaced. First thing to do is check your owners manual. Second thing is to contact Aprilair. Third thing is to repost here, with more information on what you have.
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It is model number 560, as shown here. They have a humidistat that looks like mine for $50. I'd guess I need to research it more to see if is working properly.
http://www.ontimemall.com/aprilaire560parts.html
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I have an Aprilaire that is the powered model. The humidstat goes on the cold air return plenum. There is also a temp sensor that goes outside. It's function is to reduce the humidity as the temp decreases outside. From the behavior sited, it sounds like the humidistat is bad. If it's set just short of the point where it would turn on, then with the heating system running regularly, it should come on before too long. Sounds like its broken and you essentially have just an on/off switch.
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Buck Turgidson wrote:

Hi, If the 'stat is mounted on the cold air return duct, I don't think it's measuring humidity of your living space, like your living room or hallway. Wouldn't it be common sense? Actually RH is function of DEW point which relates to temperature and moisture in the air. We are not measuring absolute humidity, we're measuring RH in this case. Tony
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Sorrr Toney, but I have to intergect. I think you have good intentions, but, not a clue as to pyhsics. Dew point has to do with the saturation point compaired to temperature, not relative humidity. Relative humidity is just that...the relatioship of dry air molecules and wet air molecules, absolute humidity has to do with the amount or wet air molecules per pound of atmosphere. Again your intentions are noble, but, you need to understand physics before you quote any!!!!! Lesson..........Dew point is the point at which saturation is reached and the temperature corisponds to allow a change of state from vapor to liquid...or...sublimation...look it up. A can of soda on a hot day causes condensation on the surface between the two temperatures allowing vapor ( water ) to change state to a liquid. The question was one of Enthalpy, ever heard of that? Before you respond do some homework and in particular the " Mollier " diagram. And do not confuse Ethalpy with Entropy...there will be a test...lol No offence intended, it is just that those that think they understand HVAC trade, dont have a clue as to the true natureof physics, or the laws of thermal dynamics. Example.....If you think you do know these things..name, Charles, doyels, and Boltons laws or pressure, temperature and volume, ......name them and I willl then be impressed
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Alice Beach wrote:

Hi, Yep, I slipped my mouth there. Should read DEW point is function of temp and mositure. PV/T=P'V'/T'? Is that Doyels? D should read B? Tony
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And exactly how you measure humidity doesn't explain the basic fact that the problem humidistat is not responding at all. The OP clearly stated that he set it just short of the point that would make it come on immeadiately. In a house where it's cold enough outside that the heating system is running frequently, the humidifier should then come on soon thereafter and start running occasionally to keep the humidity up. His humidistat only turns it either on continuosly or off, depending on where he sets it. Definitely sounds like it's failed and simple to replace.
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Thanks for reading carefully!
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Hi Tony, actually each man looked at the corrisponding change from one of the three, alladding up to the fact that if one is altered that a change occurs in one of the others. It is not a simple equation of one divided by the other, rather a ratio of what changes when one is raised or lowered. I am assuming you are a hvac tech, and if so, I applaud you. Most techs are not concerned with how things work, just what to do. Here is another test....What law is this....................The electromagnetive force is dirrectly proportional to the current flow and inversly proportional to the resistance?? Give an example of where this would apply in our field. I am not trying to show any superiority here, I am actually excited to find another tech interested in the physics of what our field is about.
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Alice Beach wrote:

...
You might get more respect if you did a spell-check, Alice...
Even giving you the occasional typo, your spelling and grammar are atrocious...
interject compared corresponds offense Doyle it's "thermodynamics" not "thermal dynamics"
And, there's a definite relationship between dewpoint, temperature (wet and dry), and relative humidity...it's how it's measured...the other is <reasonably> correct, albeit not very precisely/well stated. (That is, it's in the neighborhood, but nobody from CalTech is going to be calling soon...).
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Indeed. Td = Ta/(1-Taln(R)/9621), approximately, with the Ts in degrees Rankine and R = RH/100. For instance, 70 F (460+70S0 R) air at 50% RH has dew point Td = 530/(1-532ln(0.5)/9621) = 510.5 R, ie 50.5 F.
Nick
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You are correct,that my keyboard sticks and that I don't take time to spell check and check my grammar. Although your response included some errors....smile I say again, put down into words the " laws " of physics that you are accusing me of mis-stating. anyone can simply say you are wrong. And read the context of my words....where did I say there was not a relationship of any two laws, ie., dew point and relative humidity? If you were as good at reading comprehension as you are at spell checking, you would have heard I pointed out that r/h is not a " function " of dew point. If you are so knowledgable why not put down the truth as you see it that am wrong about instead of words with nothing but a personal statement to back them up, or are you that guy that backs things up with " I said so " statements. And last but not least......CAN YOU READ.....I stated that this is a conversation between myself and another service tech that I admire for his knowledge and quest for knowledge in our respective trade. P.S. Not planning on Cal-Tech, but dare you to put me in the lower percentile of any hvac tech you have met or had dealings with. Ask the next one to your house about the laws of physics that are the base of his/her trade, I think you will be shocked at the lack of basics they posses
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Alice Beach wrote:

...
I didn't say you were wrong exactly, just not precise nor clear...your description leaves much to be inferred that could be easily misinterpreted.
I doubt seriously I'd be shocked at all at the lack of basic knowledge of almost any segment of the general population, unfortunately. Given the level of comprehension of some of the engineering graduates I interviewed is enough to disabuse one of the thought that <all> graduates of any institution are deserving... :(
I'm only pointing out that if you have any hope of convincing anyone you really do know something, you'll have a lot more success if your postings reflect at least a <modicum> of education/care...if you know spelling is a challenge, for example, taking a little extra care would seem only prudent.
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Hi Alice, hope you are having a nice day
On 17-Dec-04 At About 02:05:07, Alice Beach wrote to All Subject: Re: AprilAire Humidistat
AB> From: snipped-for-privacy@webtv.net (Alice Beach)
AB> I stated that this is a conversation between myself AB> and another service tech that I admire for his knowledge and quest AB> for knowledge in our respective trade.
Tony hwang is not a tech and doesn't really display too much "Knowledge" of the trade.
-=> HvacTech2 <=-
.. "Everywhere is walking distance if you have the time." - s.w.
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Hi Tony, hope you are having a nice day
On 16-Dec-04 At About 01:03:01, Tony Hwang wrote to All Subject: Re: AprilAire Humidistat
TH> Hi, If the 'stat is mounted on the cold air return duct, I don't TH> think it's measuring humidity of your living space, like your living TH> room or hallway. Wouldn't it be common sense? Actually RH is TH> function of DEW point which relates to temperature and moisture in TH> the air. We are not measuring absolute humidity, we're measuring TH> RH in this case. Tony
Actually it is measuring space humidity. where do you think the return air comes from?
-=> HvacTech2 <=-
.. "And when you add them, they magically become one new number."
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As a heating and AC guy, I've installed more than several Aprilaire humidifier. Sounds like you've got a bad humidistat. Yes, it's supposed to be in the cold return side. Yes, some of them have a sensor that goes outdoors.
Yes, replace the humidistat.
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Christopher A. Young
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Stumped Moron posted for all of us....

I guess i will leave this alone because nobody can get hurt or killed by taking his advice; however wrong it may be...
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Tekkie

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