How to bypass a broken humidity controller

House Repair Talk

Help Support House Repair Talk:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

BigRich

Member
Joined
Jan 25, 2025
Messages
12
Reaction score
3
Location
North Carolina
I have a whole house Aprilaire 800 steam humidifier controlled by an Aprilaire model 62 humidity controller. It has worked fine for the past ten years but it doesn't seem to want to come on this year.

It cycles and works in test/reset mode when the dial/switch is turned to that setting but the digital number does not match the dial setting as I turn it when it is not in test mode.

In the past, I just turned the dial and paid little attention to what the digital display said so I don't know whether it should follow the dial setting but it sure seems like it should. Attached is a picture I took when I turned the dial to "7" (6 1/2). As you can see the display says "1".

After a reset the digital display seems to go higher. The last time I reset it I turned the knob slowly and the digital display reached “5” by the time the knob pointer got to “7”. Then it seems to degenerate to a lower reading. I never noticed before because you need to move the knob a little to get the digital display to switch from humidity % to the number.

Basically my questions are:
I have ordered a new controller and I won't be able to replace the one I have until next weekend. Is there a simple method to bypass this controller? I don't mean run it in manual mode, I would do that but the humidity measuring circuit thinks the humidity is just fine (actually a lot higher than it is even at the highest setting) and won't send a humidity demand to the humidifier.

If there is no relationship between the knob number and the digital reading, what do the digital numbers represent?

The manual doesn’t cover the digital readings at all (it refers to the dial/knob settings) and the unit is not functioning as it should. It has been down in the mid-teens outside and the humidity in the house is down to the mid to upper 20% range and the controller is not calling for the humidifier to come on.

Dial seven but digital one.jpg
 
Hi BigRich,
The first troubleshooting step is to ensure that there is no dust in the unit. Dust and humidistats are bitter enemies. If there is dust, blow it out very gently. A soda straw or a bulb baster helps. (Compressed air is too violent.)

Why No Dust?
Many have a flat, semi-conductive plate with two tiny wires attached. The surface of the plate's resistance changes with humidity and this varies the voltage being sent down one of the wires. If the plate gets dusty, the change won't be registered at the correct time because the dust holds humidity. Don't touch the plate & don't clean it with water or alcohol.

Others work with a single piece of human or horse hair that twists with humidity, thus the length changes. It pulls on a contact point which glides over a wire wound variable resistor. That's how my humidistat for my steam humidifier works. Any dust at all and the hair can't move.

Attached below are two documents that may help you get yours temporarily operating. Some troubleshooting is in one and the other has wiring diagrams that may help you bypass the trouble spot until your replacement arrives.

Hope This Helps,
Paul
 

Attachments

  • Aprilare-62-Install-Instructions.pdf
    1.5 MB
  • Aprilare-62-User-Guide.pdf
    364 KB
Hi BigRich,
The first troubleshooting step is to ensure that there is no dust in the unit. Dust and humidistats are bitter enemies. If there is dust, blow it out very gently. A soda straw or a bulb baster helps. (Compressed air is too violent.)

Why No Dust?
Many have a flat, semi-conductive plate with two tiny wires attached. The surface of the plate's resistance changes with humidity and this varies the voltage being sent down one of the wires. If the plate gets dusty, the change won't be registered at the correct time because the dust holds humidity. Don't touch the plate & don't clean it with water or alcohol.

Others work with a single piece of human or horse hair that twists with humidity, thus the length changes. It pulls on a contact point which glides over a wire wound variable resistor. That's how my humidistat for my steam humidifier works. Any dust at all and the hair can't move.

Attached below are two documents that may help you get yours temporarily operating. Some troubleshooting is in one and the other has wiring diagrams that may help you bypass the trouble spot until your replacement arrives.

Hope This Helps,
Paul
Thank you Paul but I already have the Aprilaire installation and user guides and they didn't have any information to help. Especially what the digital numbers represent like the large "1" in the picture I attached.

I appreciate your description of how various humidistats work. I have quite a few of them in my home and I know about the horse hair type but not the others.

I would really appreciate it if you were specific to the Aprilaire model 62. Then I would know where to attempt to clear dust accumulation. At this point I can't hurt it because it's not working anyway. The matter of testing any repair attempt is now complicated by the fact that it finally rained this morning and the house humidity is rising normally.

I am attaching a picture of the insides of my Aprilaire model 62. The picture was taken years ago and was only for the purpose of documents the wiring but perhaps you can indicate where the dust might be affecting the control? I am not sure, but I believe there is a collar on the back of the controller which may be where the air passes through. I seem to recall some mention that the unit has a gasket of sorts on the back but I haven't taken it down yet. The collar may act as some sort of filter to keep the dust out for all I know???

Humidistat wiring.jpg
 
I don't know on the Aprilaire 62 where the humidity sensor is located.

At this point, it may be worth calling Aprilaire's or Research Products Corporation technical support and describing your trouble. They are fairly helpful. (RPC owns Aprilaire) It is slightly possible that the unit simply requires a factory reset. Technical support will have the routine.

There is a very good chance that the humidistat was actually made by White Rodgers or Emerson. (My Aprilaire was Whte Rodgers in disguise.) White Rodgers has excellent technical support. Emerson = Lousy if at all. You'll have to search by photo to find a match.

About Possible Dust-
Look all around the housing for slots opposite of each other. That is a clue to where the air being sensed passes. At minimum, try to gently clear any dust from everything in the air path. Look around bezels, raised housings and such.

One thing I did notice in the photo is a rheostat. It is to the right of the screen and has OFF, A, B and C printed on the circuit board. You could try to "wipe" it clean. It may have carbon or dust build up, thus throwing false data.
How:
With the power off, mark the exactly where the dial is positioned. Using a jeweler's screwdriver, preferrably plastic, turn it gently & slowly all the way clockwise and all the way counter-clockwise a few times. Then put it back exactly where it was. Without the schematics, it is impossible to know if this calibrates the sensor or calibrates the display reading. It may or may not help solve the problem.
 
I don't know on the Aprilaire 62 where the humidity sensor is located.

At this point, it may be worth calling Aprilaire's or Research Products Corporation technical support and describing your trouble. They are fairly helpful. (RPC owns Aprilaire) It is slightly possible that the unit simply requires a factory reset. Technical support will have the routine.

There is a very good chance that the humidistat was actually made by White Rodgers or Emerson. (My Aprilaire was Whte Rodgers in disguise.) White Rodgers has excellent technical support. Emerson = Lousy if at all. You'll have to search by photo to find a match.

About Possible Dust-
Look all around the housing for slots opposite of each other. That is a clue to where the air being sensed passes. At minimum, try to gently clear any dust from everything in the air path. Look around bezels, raised housings and such.

One thing I did notice in the photo is a rheostat. It is to the right of the screen and has OFF, A, B and C printed on the circuit board. You could try to "wipe" it clean. It may have carbon or dust build up, thus throwing false data.
How:
With the power off, mark the exactly where the dial is positioned. Using a jeweler's screwdriver, preferrably plastic, turn it gently & slowly all the way clockwise and all the way counter-clockwise a few times. Then put it back exactly where it was. Without the schematics, it is impossible to know if this calibrates the sensor or calibrates the display reading. It may or may not help solve the problem.
Thanks again Paul. I will try the suggestions you made.

As far as the "OFF, A, B, C" reference. It is a switch, not a rheostat but it could still get dirty/dusty. I will try cleaning anything that might accumulate dust when I get in there. Right now my aggressiveness is quelled by the fact that our weather has changed dramatically. It rained yesterday and it is expected to be in the 60's and even one day in the 70's for the next week. Crazy weather, last week in the teens and low 20's and this coming week a burst of spring.

The switch is supposed to be set "OFF" for my Model 800 humidifier per the installation instructions (basically, set it and forget it when installed) because the 800 is a steam humidifier and has no water panel.
Water panel switch.jpg
 
Update...
This is not my humidistat but I'm pretty sure mine is the same (I found this picture on eBay).

It seems pretty obvious that the air which is being measured for humidity passes through where the black gasket is on this picture. The manufacturer thinks it is important enough to put instructions right on it saying not to install it without the gasket.

It also looks like it is not easy to remove the circuit board from the plastic housing to get a better look at exactly what is sensing the air behind where the gasket is.

For all I know there could be a blockage where the air is supposed to pass (as Paul suggested) since mine is mounted in such an odd way (in my opinion).

It was mounted by the original installers but that does not give me great confidence that it is the way the manufacturer would want it to be. Like a lot of people, I could tell you stories about terrible installations by so-called professionals.

As a matter of fact, mine could be missing the gasket completely since it seems to be mounted in a way that would have this gasket hanging out in mid air and not through a duct (see my original pictures).

Likely where the air passes through.jpg
 
Update...
This is not my humidistat but I'm pretty sure mine is the same (I found this picture on eBay).

It seems pretty obvious that the air which is being measured for humidity passes through where the black gasket is on this picture. The manufacturer thinks it is important enough to put instructions right on it saying not to install it without the gasket.

It also looks like it is not easy to remove the circuit board from the plastic housing to get a better look at exactly what is sensing the air behind where the gasket is.

For all I know there could be a blockage where the air is supposed to pass (as Paul suggested) since mine is mounted in such an odd way (in my opinion).

It was mounted by the original installers but that does not give me great confidence that it is the way the manufacturer would want it to be. Like a lot of people, I could tell you stories about terrible installations by so-called professionals.

As a matter of fact, mine could be missing the gasket completely since it seems to be mounted in a way that would have this gasket hanging out in mid air and not through a duct (see my original pictures).

View attachment 34237
If I'm reading correctly, you are referring to the item on the right in the photo. (I put a screen shot with an arrow pointing to what I'm referring.)

That is, as you suggested, the humidity sensor. My current Honeywell manual control for my steam humidifier has the same sensor.

About once a year, the unit stops calling for humidity. I gently use a bulb baster to blow the dust out of it from the top. So far, it's always started working again. I think the cans of air would be too harsh of a flow and may even freeze it because those use R-134a as the "air".

The gasket, I believe, is to ensure that only still ambient air is being sensed instead of moving air from when the furnace (or air handler in my case) is operating.

Paul
 

Attachments

  • Sensor.png
    Sensor.png
    196.5 KB
If I'm reading correctly, you are referring to the item on the right in the photo. (I put a screen shot with an arrow pointing to what I'm referring.)

That is, as you suggested, the humidity sensor. My current Honeywell manual control for my steam humidifier has the same sensor.

About once a year, the unit stops calling for humidity. I gently use a bulb baster to blow the dust out of it from the top. So far, it's always started working again. I think the cans of air would be too harsh of a flow and may even freeze it because those use R-134a as the "air".

The gasket, I believe, is to ensure that only still ambient air is being sensed instead of moving air from when the furnace (or air handler in my case) is operating.

Paul
I no longer have a bulb air blaster, I have no idea where it got lost but I have a clean and empty squeeze bottle that I can use instead.

For what it's worth, I see where that area of the back of the humidistat connects to the circuit board on the front and circled it.

Humidity sensor.jpg
 
I no longer have a bulb air blaster, I have no idea where it got lost but I have a clean and empty squeeze bottle that I can use instead.

For what it's worth, I see where that area of the back of the humidistat connects to the circuit board on the front and circled it.

View attachment 34241
I didn't think of the empty squeeze bottle. That's a great idea.
The circled part isn't what the opposite side of the sensor in mine looked like. Mine had solder tabs going to a remote I.C. chip. The solder dots on yours indicate that the front and back are two separate components, the part in the above photo being the I.C. chip and the other side doing the sensing. (The part with the gasket)

But the front of yours exactly matches mine. Cnjept was the brand name of the sensing component on mine. It was the humidity only version. (Some sense both temperature and humidity.)
 
I didn't think of the empty squeeze bottle. That's a great idea.
The circled part isn't what the opposite side of the sensor in mine looked like. Mine had solder tabs going to a remote I.C. chip. The solder dots on yours indicate that the front and back are two separate components, the part in the above photo being the I.C. chip and the other side doing the sensing. (The part with the gasket)

But the front of yours exactly matches mine. Cnjept was the brand name of the sensing component on mine. It was the humidity only version. (Some sense both temperature and humidity.)
I took it down last night and inspected it closely. I didn't see any dust or foreign particles but I air cleaned both sides anyway. Unfortunately, it made no difference that I could tell. The humidity did rise from me handling it and breathing near it but it settled back down and is still reading high. I take that with a grain of salt, as the expression goes, since the humidity should be higher since the weather changed.

I still have the concern about the digital number reading regardless of the humidity percent reading. After I remounted it and turned it back on, I turned the knob all the way up and when the knob was at 6 1/2 to 7, the digital reading was only "2".

When this was working properly, I seem to recall that the digital number was close or the same as the knob pointer but my memory is not perfect over the years since I only mess with this when it's not calling for humidity as the house dries out.

I will receive the new Aprilaire Model 62 humidistat tomorrow and I will see how that one reacts when the knob is turned.

The new one is not exactly the same as the one I have now but that goes with how things change in the different industries. According to the online picture of the new one, it has 2 less wire connectors but it shouldn't matter because those two are not connected on the one I have and all the others are labeled the same.

I hope I can post some progress by Friday or Saturday. According to the weather, I probably won't get to see if it calls for humidity for at least 2 weeks.
 
UPDATE:
Well the new humidistat arrived early so I installed it and it looks very promising.

On my old humidistat when I posted in this forum I had it set to "6 1/2" on the knob and the digital display read "1". Fiddling with it, I was temporarily able to get it to go up to around "4" (when set to "7") for a few seconds but it would go back down to "1".

I just turned the new one on and when I turned the knob to "4", the digital display also went to "4". I won't know if it works until the weather gets cold and dry again but I think it's fixed now.

Here's a picture I just took showing the digital display matching the mechanical knob setting. Fingers crossed 🤞 .

Thank you Paul for working with me on this.

0 New humidistat where 4 is 4.jpg
 
OK. I'm calling this one fixed.

I didn't expect the humidifier to come on the way the weather was going but it went down in the low 40's last night and I can see the steam canister in the humidifier dropped down to about half full and the humidistats I have all over the house are reading an average of 12% higher (around 44% now). When the old humidistat was in, it got down to 28% in the house and it wouldn't come on.

As far as I'm concerned, the digital reading should match the knob setting and my old one was just malfunctioning.

Now I learned something that I will hopefully never need again.

Off to fix the dishwasher now (I hope)!
 
I'm glad things worked out, Big Rich.

Off to fix the dishwasher now (I hope)!
Well that's quite a coincidence!
This evening our steam humidifier isn't working. I'll attack it tonight.
And, the dishwasher broke down today. That'll be a fun Saturday project. (Fun?)
Paul
 
I'm glad things worked out, Big Rich.


Well that's quite a coincidence!
This evening our steam humidifier isn't working. I'll attack it tonight.
And, the dishwasher broke down today. That'll be a fun Saturday project. (Fun?)
Paul
All our appliances are at the 11 year mark. The only one that has not had a failure or been replaced is the gas cook-top.

Refrigerator, failed several times and needed to be replaced. The replacement had a defect when it was 8 months old and had to be replaced and there were several repairs in between.
The dryer failed several times in warranty and had to be replaced. The replacement had to be repaired (electronic control board) and has since needed the drum rollers replaced on the replacement dryer. The drum rollers is about as big a job as you get on a dryer.
The washer only failed once, the drive gear for the agitator and drum started slipping (partially stripped).
Repairs too numerous to mention on the dishwasher. Latest one is the top rails for the rack. My wife found a few ball bearings in the bottom filter and that's where they came from.
We're on our 3rd crawlspace dehumidifier, and the first one needed repairs before its compressor went and the unit needed to be replaced. The coil went on the second one 5 years later and needed to be replaced. Each of the replacements were out of full warranty and they charged me about 60% for the new replacements. I hope I got a good one this time but I doubt it. Each replacement was a "new and improved" model. I think they are just fixing the problems to get them to last to end of the partial warranty which goes to six years.

All of the appliances are close to high end. The Jenn Air double oven had to be replaced for a safety recall but not until after it needed a new control board under warranty. The same control board (approximately $1,000.00 each) has gone bad twice since the replacement, both times out of warranty.

In this past summer, the entire HVAC system needed to be replaced.

The saying "they don't make them like they used to" is an understatement.

I can't imagine how much all these repairs would cost if I didn't do most of them myself. You have to believe me but I do quality work and the problems I worked on are not repeat problems except for the oven control board but that lasted about 4 years before the replaced one went bad with the same problem.

Good luck with your dishwasher repair today and your steam humidifier repair as well Paul !
 
Last edited:
You're not kidding that they don't make them like they used to.

When our refrigerator, washing machine & clothes dryer were all brand new, none worked out of the box. It took months before all were working. They're Maytag.

Actually the only way I got them fixed was to send a mailed letter to the CEO of Whirlpool explaining that my new web domain "Whirlpoolsucks dot com" would go live if there was no action within the time frame that I provided. Within days, appliance repair people were tripping over each other.

And all three break down on a very regular basis, despite whole home surge protection and redundant surge protection at each appliance. (Mechanical parts break, too. Like the drum rollers that you mentioned. What a chore!)

If I can't find the problem on a control board and repair it on the bench, I send the old ones to a rebuild place for exchange. Those seem to last longer than OEM boards and are far less expensive. The downside is that the appliance is out of service for some days. For the refrigerator I kept a board that I rebuilt as a spare and bought a spare defrost terminator at a local refrigeration supply house. It eats defrost terminators.

The old GE refrigerator was, if I remember correctly, 47 years old when we replaced it- still working fine. The old Hudson dryer was from the 1950's, also working when we replaced it. We even had a 1963 GM Frigidaire upright freezer that worked with no repairs during our tenure.

The stove, a 30+ year old Jenn Air from before Whirlpool bought the company has been fairly good except for plastic parts breaking and one downdraft exhaust motor. All parts are now obsolete. (Time to learn 3-D printing?)

Our current Roper (pre-GE, pre-Haier) upright freezer is from the 1980's and only failed once when the refrigerant oil waxed and clogged the filter-drier. That cost about $12.00 in materials and a few hours of work to fix.

The current dishwasher is also about 30 years old, so it owes us nothing. Until now, only plastic parts break (obsolete). I didn't get a chance to check it today. (No motor running on call) If it must go, we'll have a fitting memorial service for that hard working appliance.

And, I got lucky with the steam humidifier. The heating element contactor's coil failed. Fortunately, I had one that fit and was the proper coil voltage and contact rating.

The common theme for the long lasting appliances is No Electronics. My wife calls it "The E Word".

Yup- They don't make them like they used to!
 
You hit the nail on the head.

We have a Haier 5 cu. ft. chest freezer which is several decades old and has never had a problem. I think it cost about $100.00 on sale. It sits in the garage subjected to all the temperature variables alongside a Kenmore French door refrigerator which we bought in 2005 and the only problem it has had is the door gasket from constant use. Out on our screened in porch is another hundred dollar Kenmore (approximately 3 cu.ft.) refrigerator only which is subjected to even more harsh conditions since it's literally outside and it has never had an issue. Thank goodness because it has a very important job, it keeps my beer cold.

The fancy kitchen and laundry room stuff with all that "E word" stuff are the ones always breaking down.

We very much miss our old dishwasher and refrigerator from before we moved. I'd bet they are still chugging along for the new owners unless a part broke that is now considered obsolete.

You and your wife may want to add the "P word" to the things that go bad these days. The gear that went bad in our fancy washer was made of plastic or nylon, not steel.

I ordered the rails for my dishwasher and had to write to the seller to make sure they were the "upgraded" parts. Apparently they were making the replacements with iron ball bearings and the reviews said they would rust and bind badly in just a few weeks or months. They assured me the parts I will receive are steel ball bearings and not the rust prone ones.
 
You and your wife may want to add the "P word" to the things that go bad these days. The gear that went bad in our fancy washer was made of plastic or nylon, not steel.
I like that one, BigRich!
Pot metals aren't a favorite of mine either, but fortunately over the years, many manufacutrers have repalced pot metals with HDPE plastic parts . ¿¿¿¿Fortunately????

My electric lawn mower's motor hub (which holds the blade to the motor) is #06 polystyrene, which gets brittle at 20 Degrees-C. (68-F) The mower was recalled in Canada because the blades fly off when the hubs shatter. (Not recalled in U.S., despite many incident reports with CPSC.)

How much extra would the manufacturer have spent using nylon or even 6061 for that hub instead of polystyrene?
 

Latest posts

Back
Top