Introduction: Fix an Air-O-Swiss AOS 7144 Humidifier (no Mist Problem)

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Air-O-Swiss is an upscale brand of humidifier that creates a fine water mist, instead of blowing air through a wick. Unfortunately some models are prone to problems. One problem a number of people have encountered is a humidifier that no longer produces any mist (e.g., here).

If you have an AOS 7144 or similar model that no longer produces mist, and your warranty has expired, Air-O-Swiss may tell you there is no solution and you have to purchase a replacement. If so, don't give up hope! It is possible to revive a non-working humidifier and get it to produce mist again. This Instructable explains how.

Note that this Instructable assumes a moderate skill level. You should be comfortable using hand tools and a soldering iron, and be able to disassemble and reassemble moderately complex equipment. Opening up your humidifier will probably void your warranty, but if your unit is under warranty you probably wouldn't be here in the first place!

While making this repair and using the repaired unit isn't a dangerous activity for a moderately skilled person, obviously I disclaim all liability resulting from your use of these instructions. I can't be responsible if you burn yourself soldering, or if your unit ends up catching on fire, etc. Proceed with caution, and if you're not confident in your ability, seek the help of a qualified person.

Step 1: Gather the Required Tools and Parts

Items you are unlikely to have on hand are in bold.

You will need:

  • A Torx security bit (my set of security bits is shown in the red box in the photo) ($5 to $10 for a set)
  • A Phillips head bit
  • A soldering iron (Radio Shack's $10, 25 watt model is more than adequate)
  • A small amount of solder meant for electronics ($2 to $5)
  • A replacement 1 amp, 250 volt fuse (yes, 250V, even for U.S. 120V models) ($1.50)
    • If you plan to replace the existing board-mounted fuse, it is an OR5 1A 250V fuse with radial leads.
    • However, I recommend replacing it with a standard glass fuse. In that case, you will also need:
  • A fuse holder that accepts the size of replacement fuse you are using ($2 to $3)
  • Superglue or another sealing agent ($2)
  • A 2x2 inch square of non-conductive, impermeable, heat-resistant material (optional but recommended). I used rubber cut from an old bicycle tube.
  • Cleaning supplies:
    • An old toothbrush
    • Cotton swabs
    • Compressed air is helpful

You may also need:

  • A multimeter or continuity tester (this is helpful in determining if the fuse is blown).
  • A 4.5 inch length of rubber or plastic tubing, with an outside diameter of 3/4 inch or 13/16 inch. This is only necessary if you are removing the heating element. ($1.50)
  • Some extra insulated, stranded, flexible electrical wire (for positioning the fuse holder as desired).

Step 2: Open the Bottom and Assess the Damage

Unplug the humidifier. Remove the water tank from the humidifier, and dump out any excess water in the base.

Remove the plastic bottom of the humidifier. On this model, there are 5 Torx security screws that must be removed. Pull off the plastic bottom and assess the extent of any damage.

In my case, there were several different problems:

  1. The glass water tube, around which the heating element is wrapped, was cracked. This allowed water to escape, and minerals in the water created a buildup around the tube and heating element. The heating element appeared to be damaged beyond repair.
  2. The unit was not producing any mist, although the cause of the problem is not immediately apparent in these photos.
  3. The small board at the bottom of the photo, which holds the humidity sensor (labeled HS) and a thermistor (labeled TH1) had cracked and fallen off its mounting post.

You'll also want to take this opportunity to thoroughly clean whatever you can reach. An old toothbrush, cotton swabs, and compressed air will come in handy. You might want to do this outside or in a garage - it can be messy!

Step 3: Remove the Ultrasonic Vibrator Unit and Assess the Damage

Remove the ultrasonic vibrator unit, which is the large unit in the center of the humidifier that has a heat sink attached to it.

To do this, first disconnect the wires connect the unit to the humidifier. Then, unscrew the four Phillips head screws holding the unit in place. Carefully note the position of these screws! Two of them are vibration dampers, with small springs, and must be installed in the same locations when reassembling. If in doubt, take a picture for reference.

Once you've removed the ultrasonic vibrator unit, you'll have to remove its metal cover, which has two pieces attached with three different screws. The second picture shows the first cover piece removed; the third picture shows the second cover piece removed.

Note the extent of the damage to the unit. The third picture shows how water somehow leaked onto the circuit board, probably shorting connections and blowing a fuse. There appear to mineral deposits on the board. The second picture shows how some of the mineral deposits have ended up on some of the capacitors.

If you have a multimeter or continuity tester, you can test to see if the fuse is in fact blown. A working fuse should have continuity (or extremely low resistance) between its two leads; a blown fuse will not have continuity (or it will have extremely high resistance).

By removing the actual vibrator (it looks like a small speaker), you may find cracks in the seal that keeps water out of the unit. These cracks allow water into the unit. This water falls directly on the circuit board below, likely shorting some connections and causing the fuse to blow. Once the fuse flows, the vibrator unit does not operate, so water cannot be turned into mist, but the remaining electronics will continue to function (e.g. the display).

Step 4: Clean the Ultrasonic Vibrator Unit

Thoroughly clean the ultrasonic vibrator unit. Use nothing harsher than damp paper towels and cotton swabs. If there are stubborn mineral deposits, you can carefully use a pocket knife to scrape them away, but be careful not to damage the circuit board.

When you're done cleaning, it should look like the photo.

Step 5: Repair Any Cracks in the Ultrasonic Vibrator Seal

The cracks in the seal must be repaired so that water does not continue to leak into the unit. I used cyanoacrylate (superglue), although there are probably better alternatives. Whatever sealant you choose should be impermeable and not react with water, should be able to withstand the ultrasonic vibrations, and when applied, should not create any gaps between the seal and the vibrator.

Step 6: Replace the Blown Fuse on the Ultrasonic Vibrator Unit

Remove the blown fuse from the ultrasonic vibrator unit. Refer to Step 3 for the location of the fuse.

Using your soldering iron, heat the joints of the blown fuse and remove it. Strictly speaking, unless you plan to replace it with the same type of non-serviceable fuse, it is not necessary to remove the old fuse, but it is good practice.

Install a new fuse. If replacing the blown fuse with the same type, insert the leads of the new fuse into the holes, and solder it into place.

If replacing the blown fuse with a standard glass fuse and fuse holder, solder the leads of the fuse holder to existing joints on the same traces where the old fuse was located. Direction is irrelevant. You may find it helpful to extend the fuse holder leads with smaller gauge, flexible stranded insulated wire.

Optionally, you can insert a square piece of non-conductive, impermeable, heat-resistant material in the space between the bottom of the vibrator and above the circuit board when reassembling the ultrasonic vibrator unit. This will provide some extra protection to the circuit board in case the seal repairs fail or additional cracks develop and water leaks through the seal.

The second photo shows the repaired ultrasonic vibrator unit, with a fuse holder wired to the board and a rubber square inserted into the unit.

When reassembling, find a place to tuck the fuse holder out of the way, and ensure that the wires do not catch on the cooling fan, and are not squashed or crimped when reinstalling the cover. The third photo shows the ultrasonic vibrator unit reassembled and reinstalled, along with the fuse holder. Don't forget to put a fuse in the fuse holder!

Step 7: (Optional) Remove the Heating Element and Replace the Water Tube

If your glass water tube/heating element is damaged, it should be replaced. In my case, the heating element was beyond repair, so I simply removed it and the glass tube. The wires from the heating element plug into a circuit board and are easily unplugged.

By removing the heating element, the humidifier will no longer produce warm mist. The warm mist display indicator will still come on when you push the warm mist button, but it will have no effect.

I measured the length and outside diameter of the glass tube and bought an appropriate replacement at a hardware store. I suggest taking the old tube with you to compare to the available tubing in the store. The original tube is about 13/16 inch outside diameter, but you can get away with using 3/4 inch tubing.

Installing the new tube is easy: cut it to the appropriate length (about 4.5 inches, but measure it first!) and insert the ends into the hoses. Then use the spring hose clamps to ensure a good fit.

Step 8: Completion!

Reassemble everything, add water, plug it in, and try it out! Your unit should start producing mist like it used to.

My recommendation to prolong the life of the unit: when not using it, remove the water tank and empty the base of water. This means water won't sit on top of the vibrator unit, and thus can't leak through cracks in the seal.

If the seal repair fails or further cracks develop and the same problem reoccurs, the same fix should also work. If you installed a fuse holder, the job will be easier next time - you'll still need to open up the ultrasonic vibrator unit, clean everything, and fix the new cracks, but the fuse replacement won't require any soldering.

I hope this helps! My dad was very happy that his humidifier was working again. If you have questions or comments, feel free to add them below.