Air-o-Swiss room humidifier (model 7142) No mist flows

It is intersting that several folks seem to be having this problem. In early December 2009 I noticed that the replacement AOS demineralization granules were wet when I opened the sealed metal envelope. I opened a couple of others and they were the same way. After a couple of weeks after replacement, the unit started puffing steam before it stopped altogether. My husband opened the cartridge and said all the crystals were clumped to one side. I emptied out the cartridge and ran it for a few days (about 4) without any crystals until it stopped generating mist altogether. Air still flows and the heater works. But it appears that the ultrasonic disc in the bottom of the unit quit. Not sure if this was all coincidental... Especially when seeing several other people with the same problems over the last couple of months.

Tonight the AOS customer service/tech support said I shouldn't run the unit without the crystals but they appeared to be concerned about the white dust.

Anyway, the AOS U7142 has a three year warranty. If you have a receipt call customer service at 1-800-336-0326 immediately. If it is after three years they said they would charge $60 to fix it.

I would seriously not entertain purchasing an Air O Swiss unit. Their units are plagued with design flaws and it is just a matter of time before it quits. See my other posts on this and other units.


Here is my issue. If you can use a torque screwdriver you can remove the bottom and remove the simply four phipps screws and the oscilattor assembly pops right off with a simply plug. Easy as changing paper in your printer. IF Air O Swiss would give access to the source of this tidy little module we could just buy one pop it in and all would be well. I have been in touch with Air O Swiss and they are all but helpful on this. They are worried about liability and I am sure their manual has it already covered. They just don't want to be bothered for a $250 unit. Well these are hard days and this should be easily fixed by a $40 part and nevertheless the unit is flawed anyway because that white seal you see is cracked and they knew they had a problem with it and future models upgrade to a different seal. They won't even take the unit back. Yes, it is out of warranty but in this economy we fix things don't we????

Repair of the oscillator assembly in an Air O Swiss room humidifier model 7142

I had a similar problem with one of the two units (Air O Swiss room humidifier model 7142) in my home. For me, the unit turns on, the front panel works, air flows, but no mist comes out. I read Dennis Aanderud's post above and that gave me a hint for repair. I decided to open the unit and inspect the ocillator assembly to find out if it could be repaired. On inspecting the circuit in the oscillator, I found that one of the components in it, a transistor, was damaged by water leakage. I was able to successfully replace that component and the unit now works normally.

For all who wish to repair their units here are the steps I followed:

Step 1. Remove the bottom : Remove the five screws (I think the type of screw the unit has are 'Double-square' with a post in the center of the head. You can use a small flat head screwdriver that will fit in and rotate the screw. This may break the center post, but you can still screw and unscrew without any problem).
After unscrewing, apply a slight force to remove the bottom plastic and remove it only slightly from the main body. There is a fan seated in the bottom part but wires are connected to the above portion. Now, try to remove the bottom slowly and grab the fan and place it on the side.

Step 2. Remove the oscillator assembly : The oscillator assembly is the part to which the transducer is attached. Gently remove the wire connector and then the four screws and the oscillator assembly should be loose. In my case the plastic surrounding the transducer was cracked.

Step 3. Open the oscillator assembly : Remove the screw at the side and you should see the PCB. When I first saw the PCB in my unit there was water all over it (due to the filled water tank) and it had white powdery like coating on it in some places. Remove the transducer wire connector, then the two screws on the PCB, and the two screws which fix the aluminum heatsink to the case.
To remove all the white dust on the PCB I put some rubbing alcohol on it and cleaned using an old toothbrush. Water entered the assembly due to the cracks in the plastic surrounding the transducer and created this dust. I covered the crack in plastic using silicon glue.








Two major elements in this circuit which can get damaged are: [1] the ultrasonic transducer (attached to PCB by a connector) and [2] the transistor (The big black part having three leads and connected to the aluminum heat sink).

Step 3a. Check if the transistor is OK : The transistor part number is given on it's face. Mine had the letters and numbers SK C3835. I found out that the transistor is of NPN type by finding the datasheet on the Internet.

(A rectifier diode is an electronic component which has a P type semiconductor connected to a N type semiconductor. and it gives low resistance to current only when (1) P type is at higher voltage than N type by +0.7 volts and (2) current flows from P to N. The other way around it gives a very-very high resistance. An NPN transistor is an electronic component which has P type semiconductor sandwiched between two N type semiconductors. The center P type is called Base and other two terminals are called Emitter and Collector. These three terminals are marked on the PCB as 'B', 'E' and 'C' respectively. You may think of the connection between the 'B' and 'E' terminal as one diode and that between 'B' and 'C' as an another diode.)

I tried to find out if the transistor is damaged by checking the resistance between each pin both ways; The +ve connected to one of the pins and -ve connected to another one and then reversing this.
Keep the multimeter in the lowest ohms range and check the resistance between each of the three terminals of the transistor. You do not have to measure the resistance but just check if none of the readings give a small resistance value (like 0, 5, 20, 100 ohms, etc).

(With +ve lead connected to 'B' and -ve to 'E' you will not get a low resistance reading as about 0.7v must be applied before the P-N connection conducts. If the transistor is good, then I think the only way you might get a resistance value reading, with the +ve lead on the 'B' pin and -ve lead on either 'E' or 'C' pin, is if you put the ohmmeter on the Mohm scale; For all scales below Mohm it will be a 'beyond scale' reading. You may be able to use the diode checker if your meter has that functionality but I am not sure how it works when checking a transistor.)

I found that my transistor had gone bad as I got the resistance between the 'B'(Base) and 'E'(Emitter) pins around zero ohms.
I found that ebay and some other websites were selling a Sanken 2SC3835 transistor for humidifiers. So, I searched for this part on electronic component supplier Digikey.com and luckily it was available for $2.73 plus USPS first class shipping. This component had similar lettering and numbering as the original part. The datasheet of this transistor also mentions that it can be used for humidifiers. The link to Digikey page for this part is http://www.digikey.com/product-detail/en/2SC3835/2SC3835-ND/3929392

Step 3b. Check if the transducer is OK : I had two of these units. One was working. So, I tried to find out if transducer had gone bad by swapping it in the oscillator unit of the working one; and it was working. I also tried the transducer of the working unit in the damaged oscillator unit and this did not work. If your transducer is damaged you can buy one from some Korean websites. From the information (pictures) given on these websites it looks like the unit they sell would compatible. Please verify before you purchase. Here is the info:

1. http://www.lattron.com/eng/index.php
I think this company makes compatible transducers, but I am not sure.

2. http://itempage3.auction.co.kr/detailview.aspx?itemno=a591832155
This one sells similar looking transducer. The oscillator in one of the picture looks the same as in Air-O-Swiss model 7142. The site is in Korean. You may have to use a 'Buy from Korea service' like http://sasaeyokorea.com/ to purchase from here.

3. http://item2.gmarket.co.kr/English/detailview/item.aspx?goodscode=249277352
This one also seems to sell compatible transducer and looks like they ship to USA. Please verify before you purchase.

Step 3c. Check if other components are good : You can check if other elements have gone bad by using a multimeter to check for the resistance(and capacitance) values, if fuse is OK and if there is no break in connection between elements. See the connection diagram I made for the oscillator unit for the resistance values. You can find the resistance values using a resistance color code chart.

Step 4. Replace transistor : I used a de-soldering iron to remove the damaged transistor from the PCB and removed the transistor from the aluminum heatsink. In low humidity there is danger of semiconductor components getting damaged due to static buildup, so to 'ground' myself I touched the screw on the electrical wall plate before removing the transistor from its anti-static package. I did this a few more times till the new transistor was soldered to the PCB. I applied little thermal paste to its metal back and spread it in a thin layer such that it covers the entire surface (Every metal surface has tiny hills and valleys on it's surface and thermal paste is used to cover these for better heat transfer by lowering the thermal resistance between the two surfaces by filling the tiny air gaps. I used a thermal paste that is used for attaching microprocessors to their heat sink's in computers. You can buy similar or look on ebay.) Screw the transistor to the heat sink and take care that the edges are parallel to the edges of the heat sink just like the original part was attached. Using a small plier bend carefully each of the three pins from a point on the lead and to an angle just like that on the old one. Insert them in the PCB and keep leads that come out on the solder side just the same length as in the old part. Solder the leads.

Step 5. Cover PCB in plastic : I covered the PCB in plastic 'Cling' food wrap to prevent water damage and covered the transistor leads in a small length insulation tape. Make sure water does not have a path to enter and remain there. If this is unavoidable then make a hole in the plastic wrapper at a suitable spot for drainage.

Step 6. Put everything else back together : The fan has a seat in the base and also in the upper part such that both hold the fan when the unit is put back together. You may bring the unit close to the base and put the fan in it's seat in the base and join OR you can put the fan it it's seat in upper unit and then attach the base being careful that the fan does not fall out of the seat.

After all above machine was working as before. I have also posted this on my blog at http://mihiramehta.blogspot.com.

Sounds like your heater element has broken

Transistor d1289 ok

I had the same problem: the humidifier stopped producing mist. I checked all components and swapped a few with a working unit to narrow down the search. I finally found that the oscillator circuit had gone out of tune. The value across the adjustable potentiometer R2 was at 15kOhm. When I measured the working unit the value was 2.4kOhm. I adjusted R2 to obtain 2.4kOhm on my non-functioning unit and everything went back to normal. It is possible that R2 got corroded or damaged and its value changed, I might have to replace it in the future, but for now all is well.

We recently had this same problem (this is only the 2nd winter with the appliance). The humidifier would stop intermittently and when it would work, the mist was so fine...definitely not like the mist that came out when we first bought it. After looking for solutions online, I came across these FAQs.

http://www.airoswiss.net/service/faq.aspx#35
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The answers below discuss taking out the cartridge and removing 2 tbsp of the granules. Since I couldn't open the cap (the side where you refill the granules), I just whacked the cartridge on the countertop to loosen the granules I could see that were up against the mesh screen. After putting everything back, our humidifier is now producing mist as it did when we first bought it. Good luck!
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Q: No mist / unit is not working / empty indicator keeps flashing
A: Fill up the water tank. Check if water is flowing through the demineralization cartridge (attached to the water tank cap). If the water tank is full but there is only little water in the base it indicates that the water is now flowing through the demineralization cartridge.

• Wait for 15 minutes to allow the mist to come out of the unit.
• If the unit is not working and the empty light is not flashing you might have set the desired humidity too low and the current humidity level in the room is higher. That is why the unit switches off automatically.
• If the empty indicator continues flashing and the tank is full, water is not flowing through the cartridge. Exchange the cartridge or the granules in the cartridge after 2-3 months, in areas with hard water exchange the cartridge after 1 -2 months. However, the demineralization cartridge and or the granules must be exchanged at the latest after 6 months or the unit does not reach its full performance.

• Make sure the cartridge and/or granules were soaked for 24 hours, water takes longer to filter through dry granules in cartridge and into the base. Next, remove 2 tablespoons of granules from the cartridge, and throw them away. Too many granules in the cartridge it does not allow water to flow from the tank to the base.

Perhaps the problem is down to whether you live in a hard water area, I have seen recommendations for using rain water or demineralised water on other units.