Can You Use Dehumidify Mode If Your AC Has Mold? What to Do Before Cleaning

September in Japan can still be surprisingly humid. After several days of rain, my house started to feel damp, so normally I would turn on the air conditioner's dehumidify mode.

Then I took a closer look inside the air conditioner.

I could see small black spots deeper inside the unit, especially around the fan. I had already cleaned the filter, but the dirt farther inside was clearly beyond what I could safely reach.

I booked a professional air conditioner cleaning, but the appointment was postponed because of a typhoon. That left me with a very practical problem: the house was humid, but the air conditioner I wanted to use for dehumidifying appeared to have mold inside.

So, can you still use dehumidify mode?

Woman checking a moldy air conditioner on a humid rainy day in Japan

If you can see a small amount of mold inside your air conditioner, you can still use dehumidify mode when you need it. However, that doesn't mean the mold should be ignored or that dehumidifying will remove it.

If there is heavy black buildup or a strong musty smell while the unit is running, it is better to limit use and arrange professional cleaning or inspection.

In my case, the cleaning was already booked, so I decided to use dehumidify mode only when necessary and avoid trying to clean the deeper parts myself.

Three steps for dealing with mold in an air conditioner before cleaning

Why Does an Air Conditioner Get Wet While Dehumidifying?

At first, this seemed strange to me. If the air conditioner is removing moisture from the room, why does moisture remain inside the unit?

Cooling and dehumidifying work by cooling humid air. As the air cools, moisture condenses inside the air conditioner and is eventually drained outside.

This means the room can become less humid while moisture is still produced inside the unit during operation.

That is also why drying the inside of the air conditioner after cooling or dehumidifying can be useful for keeping moisture from lingering inside.

Does “Internal Clean” Remove Existing Mold?

This was something I misunderstood when I first looked at my remote control.

Many air conditioners sold in Japan have a function labeled 「内部クリーン」 or 「内部清掃」. In English, you might think of this as an internal cleaning or internal drying function.

The name can be a little misleading.

Depending on the model, this function may use airflow, heat or other features to dry the inside of the unit after cooling or dehumidifying and help keep the interior cleaner.

But it should not be treated as a replacement for physically cleaning mold that has already built up inside.

There is another important point for anyone using a Japanese air conditioner: don't assume you need to press the Internal Clean button manually after every use.

Some models start the drying cycle automatically after cooling or dehumidifying. Others require you to enable a setting or start the function manually.

If your remote has 「内部クリーン」 or 「内部清掃」 on it, check the manual for your specific model. After my air conditioner is professionally cleaned, this is one setting I plan to pay much more attention to.

What Can You Do Until the Air Conditioner Is Cleaned?

My cleaning appointment was delayed by only a few days, so I didn't want to turn a short wait into a DIY air conditioner project.

When the house feels uncomfortably humid, I use dehumidify mode when necessary. After using it, I follow the instructions for my unit's internal cleaning function.

I also use a fan to keep air moving and run ventilation fans where appropriate.

If you have a separate dehumidifier, that is another useful option while waiting for the air conditioner to be cleaned.

For a short period, the goal doesn't have to be making the entire house perfectly dry. Keeping damp items from sitting around and preventing air from becoming trapped in closed spaces can also help make the room more comfortable.

Should You Clean Mold Deep Inside the Air Conditioner Yourself?

Seeing black spots inside an air conditioner makes it tempting to reach in and clean them immediately. I felt exactly the same way.

I stopped after cleaning the removable filter.

Filters are designed for routine household maintenance, but the fan, heat exchanger and other internal components are different. If the dirt is deeper than the areas your manual says you can maintain yourself, it is better not to force brushes or other tools inside or take the unit apart.

Since I already had a cleaning appointment booked, I decided to leave the deeper parts alone and wait.

That was also more practical for me than risking damage to an air conditioner just a few days before it was going to be professionally cleaned.

Mold and Dehumidify Mode: The Simple Takeaway

Living in Japan has taught me that the end of summer doesn't always mean the end of indoor humidity. Long periods of rain and typhoons can leave the house feeling damp well into September.

If you notice a small amount of mold inside your air conditioner, you can still use dehumidify mode when you need it. But dehumidifying does not clean away existing mold.

If cleaning is already scheduled, use the air conditioner only as needed, avoid taking apart areas that are not meant for routine maintenance, and use fans, ventilation or a separate dehumidifier when possible.

After the air conditioner has been cleaned, check how your model handles internal drying after cooling and dehumidifying. Some Japanese units do this automatically, while others need a setting or manual operation.

And if you see extensive black buildup or notice a strong musty smell when the air conditioner runs, limit use and consider having the unit professionally cleaned or inspected.

For me, the biggest lesson was simple: dehumidifying the room and cleaning mold from inside the air conditioner are two different jobs. Once I separated those two problems, it became much easier to decide what to do while waiting for the cleaning appointment.

References

  • Daikin Industries — Air Conditioner Care and Cleaning Information
  • Daikin Industries — Air Conditioner Mold and Internal Cleaning Information
  • Panasonic — Air Conditioner Cleaning and Maintenance Information
  • Panasonic — Air Conditioner Internal Cleaning Features

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