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We've been using a Hitachi Split Inverter Type Air Conditioner for over a year now, and we recently had it service cleaned about three months ago (the recommended schedule is every eight months).

However, we recently noticed that some water droplets are forming inside the air conditioner: the first is on the metal grill-like section behind the two removable air filters, and the second is on the ceiling of the opening where the air is blown.

Another problem we noticed is that after a few days of being turned on, the air flow becomes irregular, as if the engine is having difficulty blowing air (e.g. instead of a steady "whiiiiirr," we get a "whirr... whirr... whirr...").

Based on the manual, the only maintenance we are allowed to do is just to remove the two air filters, rinse and dry them, and then put them back. Any other maintenance needs to be called on their service department. This seems to be so the warranty does not become invalid and for inexperienced users to avoid damaging the units.

Because of how limited the recommended maintenance is on the user's side, the only option we've tried is to just turn off and unplug the unit for some time (e.g. overnight or for two days). This seems to resolve the issue temporarily, but it keeps coming back.

Our first hunch is that some cooling and drain parts have frozen over, which is causing some water to collect, but water leaks very rarely and we only keep our unit in Dry mode. The drain tube needing cleaning might also be a possibility, but we haven't checked yet because, as mentioned above, we recently had the indoor and outdoor units service cleaned about three months ago.

Any idea as to what could be causing water droplets to form despite the unit being in Dry mode, and any advice on our situtation?

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Ok, you don’t understand the modes of operation. Dry mode will remove humidity thus making the coils cold attracting moisture, the cold may cause the condensation you are observing.

Run the system normally if you want cooling run it in that mode, heat should never produce moisture inside but may build up on the outside unit and then it will go into defrost.

When in cooling mode if your inside unit ices up the filters are the normal thing to check and if dirty the low air flow will cause icing.

If you have clean filters of the proper type the inside unit should not ice up. Putting in high end filters that filter everything out can reduce the air flow and cause icing. Use the filter type recommended by the installer/ manufacturer.

If the above precautions of a clean filter / proper filter are observed and the system is icing up there is a problem with the unit it could be under or over charged, one of the temp/pressure sensors failing since an inverter type.

You said it was not leaking but if the drain gets plugged with mold (a common occurrence in the cleanest homes) you should be allowed to clean the drain pan and use an approved mold inhibitor to prevent mold from blocking the drain and it overflowing.

With all the above in dry mode I would expect the unit to collect moisture ( the brands I install do).

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  • Thanks for the answer! We also contacted the manufacturer and will get back once we figure out what the problem was. We were using Dry mode because when we set the unit to Cool, our walls form water droplets due to the humidity (we assume).
    – Floating Sunfish
    Commented Feb 16, 2021 at 9:49
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    Your air flow needs to be diverted away from the walls anytime a cold surface is in a humid environment moisture will form. When I leave my split in cool mode the drains outside have a constant dribble of water from the moisture being removed from the air.
    – Ed Beal
    Commented Feb 16, 2021 at 16:50
  • Ah, I see. We'll keep that in mind. One last question, but is there a rule of thumb where air conditioners have to be turned off for a set period after being on for a certain amount of time? We pretty much keep our unit running nonstop and only turn it off for about half an hour when we clean the air filters every two weeks. Is that overworking the unit and could that cause damage over time?
    – Floating Sunfish
    Commented Feb 17, 2021 at 1:44
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    The off topic is to allow the pressure in the compressor loop to equalize so it is not trying to start under load. Leaving it running 24-7 is fine as long as outside temps do not drop low enough to cause ice at night.
    – Ed Beal
    Commented Feb 17, 2021 at 14:00
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    As far as normal run time I run my systems 24-7 in the summer, I live in an area that cools at night in the spring and fall so I only run it when needed. Some systems say not to run in cooling mode below 45f this is to prevent icing. But if the temps are high and you need the cooling just clean the filters more often, I have a horse riding arena in my back and side yards sometimes I have to clean filters in 2 weeks if they have not been watering the arena to keep the dust down.
    – Ed Beal
    Commented Feb 22, 2021 at 14:12

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