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Thread: Mr Slim Mitsubishi Mini Split - Humidity and Smell

  1. #1
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    Mr Slim Mitsubishi Mini Split - Humidity and Smell

    Hi Everyone ...

    I had a Mitsubishi Mini Split (MUZ-D30NA & MSZ-D30NA) installed a little over a year ago. Under certain conditions we get a musty/damp smell. It's a crusher for us allergy sufferers. A little background: Im here in Central Florida and use it for a room (2515) that was once a porch and converted to a room. When we bought the house, we had the open wood beams (flat roof) enclosed with drywall, added significant insulation, and had all 6 windows replaced with higher end double pained windows.

    Our problem centers around a foul smell during certain conditions. Here is an example that will trigger the problem: The outside temperature is 80 and we want to cool the room to 76. The unit will cool it down to 75-76 degrees and all is well doing so. But now that the inside temperature is at 76, its just a matter of time before a pungent / moldy odor occurs. Its so noticeable that our separate air purifier notices it, lights up, and kicks into high gear. Our digital thermometer shows the room humidity higher than it was before the unit cooling the room down. If its 90+ degrees out and the unit is running to keep it 75 or 76 degrees, there is no odor. Again, when the change in temperature (delta) from outside to inside is minimal it happens like clockwork. Hence, the issue is worse at night, when its 78 out and we want the room at 75 or 76 degrees.

    Workarounds:
    • Switching the unit to dehumidify mode, clears the smell.
    • Dropping the temperature, clears the smell.


    Impact:
    • We can never set the unit in auto mode (setting 1 on the remote) , where it can keep it at a comfortable 76. It will sit there in a low throttle and stink up the room.
    • In cool mode, we have to lower the temperature, and everyone freezes.
    • In a typical night, we set it on 76. When it gets to 76, after a short time, the room starts smelling. I then flip it to dehumidify mode, it drops the humidity, drops the temperature, and the smell goes away but we freeze. I turn the unit off until we warm up, then restart the whole process again. Likewise, I can drop the temp to 74 for a short time to help combat the smell. We have done this for the past year and I am exhausted.
    • I dream of the day of being able to set it at 76 and just forget it.


    Other important notes:
    The issue is not that the unit is dirty and omitting a smell (irregardless of the temp). We had it cleaned and there is no change.
    If the issue was that I have an overly humid room, why is there no smell when I enter the room in the morning with the AC off all night? The humidity in the room shows 47% on an average morning. When I run the AC for a short time at 76, the humidity rises to say 55% and then starts spitting out a pungent smell.

    The problem that I have perceived from day 1 (an oversized unit), still remains to me like the culprit. I have read several times that if the a/c unit is too large for a space it cools the air quickly and doesn't stay on long enough to drop the humidity to the appropriate comfortable level. I highly value our "Diamond" installer, but he disagrees that an oversized unit is an issue.

    The installer reached out to Mitsubishi and they wanted to try a workaround of setting a jumper that turns off the inside fan once the unit hits the target temperature. We are giving it a try, but it's not going to be a fix. It might help a little, but the unit still starts to omit a foul smell and the room humidity still rises significantly. I don't think it reacts quick enough before the condition presents itself. If mother nature allowed it to always be 95 degrees outside, then this might help us around the problem. But when you have the unit trying to keep the room at say 75 or 76 degrees and it's 79 out, it's the recipe for disaster.

    Thanks in advance for any guidance.

    Regards,
    Rob

  2. #2
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    One addition ... (pls forgive my layman's terms, as I attempt to describe this from this ordinary homeowner ...) In talking to our installer, his communication of the issue to me is the outside unit will run at say a speed of 90 ("high gear") when it detects that it needs to get the indoor temperature from say 80 down to 75. Once the difference in target temperature and actual temperature get closer, the outside unit "gets more efficient" and starts to throttle down to say 50, 40, 10 ("low gear"). So the outside unit is running very low or off (not as cold coil), but the inside fan continues to blow, but now more more mild air. The net effect is higher humidity and the unit starts pumping out unpleasant smelling air.

  3. #3
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    Attempting to post a visual, as I just did a "test case" this morning. I had the temperature pegged on 76 degrees in auto mode. Humidity continues to climb ... from 52% to 58% in a little over 90 minutes.

  4. #4
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    Most likely microbial growth on the coil and/or wheel. n my experience options include adding chlorine tablets to the coil, chemically cleaning the coil/wheel or installing an air purifier specifically designed for mini splits.
    ...

  5. #5
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    What causes the odor?
    In order to find a permanent solution to the Dirty Sock Syndrome, it was first necessary to understand how the odor was generated. Curiously, the cause of the problem all along was the simple growth of mold and bacteria on the coil, as indicated by the effect of early cleaners.
    Heat pumps were particularly susceptible because, unlike conventional heat exchangers, their heating cycles were not hot enough to kill the microbes that thrived on their wet coils during the cooling season. Instead, the temperature was just warm enough to slowly “cook off” their organic odors, producing that gym sock odor.


    Adding to the problem were the water and organic debris in the drain pan, which formed a fertile garden of microorganisms. The slow warming of this contaminated water released a plethora of spores and toxins into the air that served the conditioned space.


    Why the problem appeared during the heating season was linked to the “reverse mode” operation for defrosting the outdoor coil. This process generated moisture on the indoor coil, giving dormant microorganisms and residual organic matter new life, and providing a simple but effective odor release and carrier mechanism.


    In today’s high-efficiency units, the old problem is exacerbated. Larger coils and more closely spaced fins create an expanded surface area to retain even more organic material.


    In addition, they retain more moisture, stay wet longer, and their drain pans hold more water and organic debris. All of these factors contribute to a longer and more productive cycle of microbial activity.


    This greater activity equates to more spores, toxins, and odors for a longer period of time.

  6. #6
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    Why is mold so difficult to control?
    Mold is at the bottom of the food chain. It thrives on very little, grows rapidly, and produces spores, volatile organic compounds, and other toxins. One organism can multiply to trillions in less than three weeks.


    And mold occurs everywhere — in hvac systems in homes, schools, workplaces, entertainment centers, vehicles, etc. They all are mold reservoirs.


    As noted above, a/c equipment interiors provide an ideal environment for mold growth — it’s dark, damp, and filled with nutrients. The result can be like blowing air over a swamp or through a sewer and then into our homes, vehicles, and workplaces.


    According to the World Health Organization (WHO), 60% of IAQ problems and allergies may be mold-related. Some IAQ diagnosticians and practitioners today say the figure may be as high as 80%. The increased usage of air conditioning systems (installed base) almost directly parallels the increase of allergies and IAQ problems.


    As mold and bacteria grow on coils and in drain pans, they are disseminated through the ducts to occupied spaces. Some mold products (toxins) produce serious and sometimes life-threatening reactions, including allergy, asthma, hypersensitivity pneumonitis, and even bleeding lung disease.


    Additionally, mold creates a troublesome maintenance problem. Its activity results in dirty coils, an increase in pressure drop, loss of heat exchange efficiency, dirty and sometimes plugged drain pans, and excessive energy use.

  7. #7
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    Using UVC
    Accurate Environmental Systems has found that the most successful way to handle system mold is through continuous source control using hvac-style UV germicidal lights.
    Ultraviolet light in the “C” band (UVC) has been used for more than 65 years to kill microorganisms in hospitals, laboratories, food processing, and pharmaceutical plants, and even at the nation’s Center for Disease Control.


    However, conventional UVC products are limited to still air applications where ambient temperatures are of 80° to 90°F, and are therefore not effective in the cold and moving temperatures found where mold grows in hvac systems.


    As a result, our company has standardized our use of a new generation of patented UVC lights that are specially suited for installation at the coil and drain pan area, to eliminate mold and bacteria right at the source.


    Steril-Aire, Inc.’s UVC Emitter™ has been independently tested and proven to produce up to seven times the output of conventional UVC devices in the cold, moving air environments of hvac systems, eradicating mold and bacteria quickly and effectively.


    The UVC energy attacks the organism’s DNA and either kills it immediately or prevents it from reproducing. Continuing exposure degrades the carcasses and any other organic material through vaporization (without heat), cleaning the coil to “as-new” specifications.


    Emitter tubes typically last more than 7,500 hrs (“on” time), or slightly over one year. The lights pose no danger to equipment, individuals, or furnishings, and there is no risk of secondary contaminants such as particles, ozone, or chemicals being released into the system or space.


    For our first UVC customers, the original motivation for installing the lights was to abate IAQ complaints and/or allergies. What we didn’t anticipate when we started working with UVC lights was the elimination of Dirty Sock Syndrome and the return of system efficiency.


    In place of the unwanted smell, customers have repeatedly told us that the lights produce a clean, fresh air sensation in their buildings and homes.


    Another unexpected benefit has been the complete removal of all the organic material typically found in the interior of the coil and plenum area and in the drain pan. The UVC devices thus eliminate coil and duct cleaning, as well as the use of drain pan tablets and biocidal agents.


    We have found that the pressure drop across the coil returns to the original design specifications or, stated another way, heat exchange efficiency and system capacity return to “as new.”

  8. #8
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    All this and IAQ
    The new UVC technology also does what it was originally designed to do: enhance IAQ and reduce the incidence of allergy and illness.
    To cite an example, a residential customer named Laura Toms was acutely ill with what had been diagnosed variously as Chronic Fatigue Syndrome, allergies/environmental illness, and Multiple Chemical Sensitivity. After allergy testing revealed a strong sensitivity to mold, we recommended use of UVC Emitters in her Columbus, Ohio home.


    About six weeks later, she wrote, “Since you installed the UVC system, I believe I have recovered to the point of being 90% cured, and improving all the time. If you ever had to live with the debilitating fatigue, temperature fluctuations, sore throats, and other symptoms I’ve endured, you’d realize how thankful I am to feel normal again.”


    An average installation of UVC Emitters will kill up to 90% of the “fly-by” bacteria and viruses passing through the system. This reduces the recirculation of colds and flu virus or any other airborne disease through the hvac system. If used to control infectious diseases such as TB, the UVC system can be designed to eliminate more than 99% of the bacteria for the greatest level of protection possible.


    Given their multiple benefits, we have found that UVC devices are one of the most innovative maintenance and control items to hit the hvac market in years.


    A properly designed and installed UVC system will provide your customer with healthier, more energy-efficient and productive environments, while removing those dirty socks from their air conditioners.

  9. #9
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    Ref: http://www.achrnews.com/articles/114...-sock-syndrome


    Also, your unit is a 2.5 ton inverter unit that can modulate down to just under 1 ton of cooling. Like kangaroogod stated you have bacteria on your indoor coil. You need to have the coil professionally cleaned with the proper cleaner that will not harm the system but will kill the bacteria. DO NOT USE BLEACH!

    Also, your A/C has a built in condensate pump which makes matters worse, In a straight drain line system moisture travels down a sloped drain pan and outside through a condensate line, in yours the water has to build up to activate a float switch, then the condensate pump will pump all the water out, this pump builds up mold and algae in the reservoir that will infect your whole system, its like a disease.

    Also: http://www.mitsubishipro.com/media/2..._submittal.pdf

  10. #10
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    Thank you all very much for the insight. I need to reread it all and try and digest it. Note, we just had the unit cleaned. The installers took the inside assembly apart and cleaned it thoroughly. Note though, this odor issue has been there since day 1. Cleaning the unit had no positive effect.

    The drain situation was a challenge from the beginning. It drains out the back of the wall, through a closet, then through an exterior wall. Early on we had quite the hiccup as it was "double trapped." It caused the unit to backup and drip water and ruin our big screen. They took care of it no questions asked, which goes hand in hand with the way these guys do business. I wonder though if there is something going on with the drain line as noted directly above.

    The part I still would like to address is the increased humidity. Is this normal? I ask because the smell and the increased humidity go together hand in hand.

    I ran another test this morning. I set the fan on COOL AUTO at 76 degrees. I left the AC alone for over 90 minutes. More odor and higher humidity as time progressed.

    • AC off all night
    • 8:59AM: Outside: 80 degrees / 92% humidity ... Indoor: 77 degrees / 52% humidity
    • Set AC to 76 degrees.
    • 9:57AM: Outside: 81 degrees / 89% humidity ... Indoor: 76 degrees / 53% humidity
    • 10:13AM: Outside: 81 degrees / 88% humidity ... Indoor: 75 degrees / 55% humidity
    • 10:36AM: Outside: 82 degrees / 87% humidity ... Indoor: 74 degrees / 58% humidity



    Thanks,
    Rob

  11. #11
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    Have you tried setting the temp at 80^F and dehumidification. The net result cold be overcooling to 77^F in the slow cooling dehu mode. Also consider adding a separate dehumidifier to the space set at <50%RH.
    There could also be building involvement. The sun on the outside of structure can drive the exterior moisture to the cool inside surface, causing long term condensation on the cool surfaces, like dry wall and behind pictures/mirrors.
    Sounds challenging, follow your nose. Keep the interior warmer and drier when not in use will also help reduce odor producing biologicals. Where in FL?
    Keep us posted.
    Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
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    Hey Teddy Bear ... When you set this Mitsubishi to dehumidification, you cannot set a temperature. We keep the unit set in this mode a vast majority of the time. It never smells in this mode, but it just gets FRIGID.

    I went and bought a room dehumidifier. It does a decent job of keeping the humidity in check when the situation described above happens ... but ... just too noisy, despite it supposedly being one of the quieter ones. We live in this room. It's my office during the day and our tv room too. There was already a window unit that cooled the room adequately, but we decided on a mini split to combat the noise. It just doesn't seem right to have to run a dehumidifier to counterbalance a mini split that (to me) is introducing the problem.

    If it weren't for the flat roof, I would have had duct work ran and never pursued a mini split.

    We are in Longwood, FL (just north of Orlando).

    Thanks,
    Rob

  13. #13
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    Make sound surround around the dehumidifier to muffle the sound. The dehumidifier should only operate when the a/c is not cooling a high load and maintaining low %RH..
    Baffling?
    Keep us posted if you figure it out.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  14. #14
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    Everyone is too smart for me I would just clean the coil and BLOWER WHEEL.

  15. #15
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    Thanks toocoolforschool ...

    I just had the unit cleaned. I know they took the blower assembly (if that is the right term) out and cleaned it. In terms of the coils, I need to confirm. As i noted though, this thing has produced the smell (under the conditions described) from very early on.

  16. #16
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    An additional comparison point. We still have the el cheapo window unit in this room and it has not been used in ages (due to the noise). I just turned it on and let it run for a while. It drops the temperature AND drops the humidity, leaving a very pleasant feeling room with absolutely no smell. This dang mini split can handle the cooling just fine, but it butchers the humidity and causes quite the smell.

    A few responses from our installer on earlier comments made here:

    "It is the ability of this unit to drop to less than one ton that means it is not oversized.
    "I believe we have now cleaned this coil a couple of times."
    "Your model unit does not have a pump. Only the ceiling cassette uses a pump. Yours is what he refers to as a straight drain line."

  17. #17
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    while I agree that suplimental dehumidification may be required, you still will have odor issues. I have installed 3 rgf minisplit Air purifiers in 2 seperate homes and have had rave reviews. it may or may not solve your situation but something to consider.
    ...

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