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Thread: Dusty/musty Smell When A/c Comes On

  1. #1

    Question Dusty/musty Smell When A/c Comes On

    I PURCHASED A BRAND NEW HOME 2 YEARS AGO. WE HAVE 2 ARMSTRONG FURNACES, ONE IN THE ATTIC, ONE IN THE BASEMENT. ABOUT 3 WEEKS AGO WE STARTED SMELLING A MUSTY/DUSTY ODOR WHEN THE A/C COMES ON. IT DOESN'T REALLY SMELL WHEN JUST THE FAN IS ON, ONLY WHEN THE A/C KICKS IN. OUR BASEMENT IS A DAYLIGHT BASEMENT WITH HUMIDITY OF 40-45%. WE USE A WHIRLPOOL DEHUMIDIFIER. THE BASEMENT HAS NO MUSTY/DUSTY SMELL WHATSOEVER.
    I HAVE SEVERE ASTHMA AND ALLERGIES, SO I AM ALWAYS USING CLOROX TO CLEAN. WE USE HEPA FILTERS ON THE FURNACE WHICH ARE CHANGED EVERY 30 DAYS.
    THE ATTIC FURNACE SMELLS DUSTY LIKE THE ATTIC, WE HAVE CHECKED ALL THE VENT CONNECTIONS AND THE FURNACE IS ALL FOIL TAPED TIGHTLY.
    I AM OUT OF IDEAS... EVEN MISTING THE AIR FILTER WITH CLOROX/WATER DIDN'T HELP.

    IF ANYONE HAS ANY IDEAS AT ALL, MY ASTHMA DOCTOR AND I THANK YOU GREATLY!!

  2. #2

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    There's only one thing that makes this dusty/musty smell, and that's mold growth. It is fairly typical for mold to grow in the evaporator drain pan and on the evaporator coil fins. The evaporator coil is located inside the air handling unit. If you follow the two copper Freon lines (one insulated, one bare) to the air handling unit(s), they terminate right on the evaporator coil. There should be a large plate that you can remove to access the coil and it's associated drain pan inside the unit. There's a drain on this drain pan that exits the air handling unit. It should be confirmed also that this drain is running free. The unit should also be pitched so that the drain pan can never have a low corner in which water will lay and grow mold during the off cycle. There are commercially available evaporator coil cleaners, which can also be used to clean the drain pan. These have a pleasant odor, and sanitize well. If the odor of Chlorox is not objectionable to you, you could use that as well. The cleaning of the evaporator coil is reccommended to be done on a yearly basis, ESPECIALLY if someone in the house has breathing problems like asthma. If this work seems beyond what you'd like to take on, contact a local HVAC company. They all have a flat fee for yearly maintenance on your equipment, which will include evaporator coil sanitizing.

    OH, I just remembered. At HVAC supply houses they sell a tablet that you can put inside the unit right in the evaporator coil drain pan. This inhibits the growth of molds and such. Don't confuse the evaporator drain pan (inside the unit) with the auxillary drain pan (under the unit) which is normally used in attic units to contain any possible leaks from the unit. There's no maintenance required for an auxillary drain pan.

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