Results 1 to 20 of 20

Thread: Musty smells from the vents

  1. #1
    Join Date
    May 2022
    Posts
    11
    Post Likes

    Confused Musty smells from the vents

    I have a 10-year-old dual-zone Carrier unit. I live in Orange County of southern California. Starting from 3 months ago, I got some musty smells from the AC vents. The smells are stronger the first few seconds when the AC is turned on; it's barely noticeable when the AC is running hard to cool down the room; but it'll get noticeable again when the compressor is off and the fan is running. The drain lines are super clear, the evaporator coil looks clean, the drain pan is mostly dry (with some minor standing water spots), the condensation trap is working, the AC blows cold, etc. But, there's very little condensation water coming out of the primary drain line (the secondary drain line is dry). Everything appears good except for the musty smell.

    I called three HVAC technicians to check the smell, but none of them could figure out why.

    After doing lots of research by myself, I found that the smell is probably from the evaporator coil. It's a horizontal N coil in the attic. When I opened the coil panel, I could smell the same musty thing as I got from the vents. When I gently tapped the fins of the evaporator coil, I could get quite some condensation water, even though the AC hadn't been run for more than a day. The condensation water held in the evaporator coil seems to provide an environment for mold/bacteria/etc. that results in the smell, although the evaporator coil looks clean with no visible molds or dirt. Also, this seems to explain why I get so little condensation water out of the drain line (only a few drops at most when I run AC for 5-10 minutes).

    I'm using 3M Filtrete filter with MPR rating of 2200 (~ MERV 13) and change it every three months. I read online that this high rating filter may restrict airflow and cause frozen evaporator coils. My evaporator coil doesn't seem to be frozen yet, but maybe it's still cold enough to hold condensation water instead of letting it drip down to the pan and drain? But, when the AC is not running, the water should still drip down? In my case, the water seems to be trapped inside the evaporator coil... (BTW: One vent that's blowing the strongest musty smell also has the coldest air... It's so cold that one can't stand underneath it for a long time..)

    Can anyone share some thoughts on the possible causes for the musty smell? Thank you!

  2. Likes cherylsmith liked this post.
  3. #2
    Join Date
    Jan 2006
    Location
    In a land far, far away
    Posts
    17,477
    Post Likes
    Yes, get rid of the Filtrete filter, they are too restrictive. You'll need a bag or media type filter for a MERV rating that high. They have far more surface area to compensate for the more restrictive filtration. They usually require some simple duct modifications, though.

    The musty smell is likely what we call "dirty sock Syndrome", and it's probably due to the evaporator coil and drain pan needing a proper cleaning with the right chemical. Any good HVAC tech should know how to do this and which product to use.

    You might also consider a UV light in the system to prevent mold and mildew in the evaporator section. These typically need to be professionally installed.

  4. #3
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Special-K View Post
    Yes, get rid of the Filtrete filter, they are too restrictive. You'll need a bag or media type filter for a MERV rating that high. They have far more surface area to compensate for the more restrictive filtration. They usually require some simple duct modifications, though.

    The musty smell is likely what we call "dirty sock Syndrome", and it's probably due to the evaporator coil and drain pan needing a proper cleaning with the right chemical. Any good HVAC tech should know how to do this and which product to use.

    You might also consider a UV light in the system to prevent mold and mildew in the evaporator section. These typically need to be professionally installed.
    Thanks a lot for your quick response!! I'll order new filters right away. The coil looks quite clean, with no visible signs of mold or dirt. I guess it's probably the standing condensate water held in the evaporate coil that's causing the bacteria growth and musty smell? Does the standing condensate water have anything to do with my air filter? Will cleaning the coil solve the standing water issue?

  5. #4
    Join Date
    Jan 2006
    Location
    In a land far, far away
    Posts
    17,477
    Post Likes
    Quote Originally Posted by greatman View Post
    Thanks a lot for your quick response!! I'll order new filters right away. The coil looks quite clean, with no visible signs of mold or dirt. I guess it's probably the standing condensate water held in the evaporate coil that's causing the bacteria growth and musty smell? Does the standing condensate water have anything to do with my air filter? Will cleaning the coil solve the standing water issue?
    You shouldn't have much standing water. Makes me wonder if the coil is not level.

    Depending on your setup, a restricted filter could affect pan water levels while running, but not when the unit shuts off.

    I think the coil needs to be cleaned regardless.

  6. #5
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Special-K View Post
    You shouldn't have much standing water. Makes me wonder if the coil is not level.

    Depending on your setup, a restricted filter could affect pan water levels while running, but not when the unit shuts off.

    I think the coil needs to be cleaned regardless.
    Thanks! I'll clean the coil again. I did some cleaning by myself a few days ago, but not very thoroughly. When I was cleaning the coil using a sprayer, the water was able to drip off the coil, though I think some water was collected inside the coil.

    The unit had been running without any problem in the last few years; it only started to have the musty smell problem from the beginning of this year. At that time, I thought it was because of the condensation trap that was not able to trap water to isolate the attic air and AC air, so I replaced it with a good EZ trap. There was plenty of black mold inside the old trap.

    Hopefully, it's not the evaporator leveling issue, and the smell will be gone after cleaning.

  7. #6
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Special-K View Post
    You shouldn't have much standing water. Makes me wonder if the coil is not level.

    Depending on your setup, a restricted filter could affect pan water levels while running, but not when the unit shuts off.

    I think the coil needs to be cleaned regardless.

    BTW: I was thinking of having the evaporator coil cleaned and disinfected by someone using a steam cleaner. Will the high temperature (say 300F) damage the coil?

  8. #7
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    38,065
    Post Likes
    Quote Originally Posted by greatman View Post
    BTW: I was thinking of having the evaporator coil cleaned and disinfected by someone using a steam cleaner. Will the high temperature (say 300F) damage the coil?
    Temperature no
    How its fine ?

  9. #8
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by pecmsg View Post
    Temperature no
    How its fine ?
    I've actually seen a few YouTube videos of steam cleaning evaporator coils, like this one: "STEAM CLEAN/ DISINFECT INDOOR HVAC SYSTEM EVAPORATOR COIL. KILLS MOLD, FUNGUS, BACTERIA & VIRUSES." (sorry, unable to post links yet)

    But this doesn't seem very common, so I'm also concerned with its potential damage to the coil and suction/liquid lines...

  10. #9
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    38,065
    Post Likes
    I've seen Boobtube videos showing all kinds of things!

  11. #10
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Special-K View Post
    You shouldn't have much standing water. Makes me wonder if the coil is not level.

    Depending on your setup, a restricted filter could affect pan water levels while running, but not when the unit shuts off.

    I think the coil needs to be cleaned regardless.
    The condensate water seems dried out today. It's been nearly four days since we ran the AC last. Quite a bit of condensate water was seen between fins inside the evaporator coil after 1-2 days of running the AC. So, I was wondering how long the condensate water would normally stay after running the AC? Is 1-2 days normal?

  12. #11
    Poodle Head Mikey's Avatar
    Poodle Head Mikey is offline Membership Chair/ARP Committee / Professional Member*
    Join Date
    Sep 2002
    Posts
    33,087
    Post Likes
    In addition to these things: make sure the drain pan drains completely. It wants to be pitched towards the drain to allow for this.

    Does the drain line have a trap in it?

    PHM
    -------


    Quote Originally Posted by Special-K View Post
    Yes, get rid of the Filtrete filter, they are too restrictive. You'll need a bag or media type filter for a MERV rating that high. They have far more surface area to compensate for the more restrictive filtration. They usually require some simple duct modifications, though.

    The musty smell is likely what we call "dirty sock Syndrome", and it's probably due to the evaporator coil and drain pan needing a proper cleaning with the right chemical. Any good HVAC tech should know how to do this and which product to use.

    You might also consider a UV light in the system to prevent mold and mildew in the evaporator section. These typically need to be professionally installed.
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  13. #12
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    In addition to these things: make sure the drain pan drains completely. It wants to be pitched towards the drain to allow for this.

    Does the drain line have a trap in it?

    PHM
    -------
    Yes, the drain pan looks good. There's an EZ trap next to the drain pan. If I pour some water onto the pan, it'll drain to the outside quickly.

    There's some rust on the drain pan. There's also a little bit of condensate water even 1-2 days after running AC, but I guess this is because of the standing condensate water trapped inside the evaporator coil. Other than this, the pan is good.

  14. #13
    Poodle Head Mikey's Avatar
    Poodle Head Mikey is offline Membership Chair/ARP Committee / Professional Member*
    Join Date
    Sep 2002
    Posts
    33,087
    Post Likes
    I wouldn't think so; no.

    Modern coils have a pretty close fin spacing - this is so they can have more surface area for heat exchange in a smaller physical space. So capillary attraction becomes a greater factor with higher efficiencies.

    The coil and the drain pan wants to first be Clean of everything. Residual oils, organics of every kind, as well as dust and dirt. And then it wants to be treated with a wetting-agent product - to promote 'sheeting' of the water rather than what might be called 'bunching' of the water.

    Is this a heat pump system? They have an additional problem in this regard.

    PHM
    --------



    Quote Originally Posted by greatman View Post
    The condensate water seems dried out today. It's been nearly four days since we ran the AC last. Quite a bit of condensate water was seen between fins inside the evaporator coil after 1-2 days of running the AC. So, I was wondering how long the condensate water would normally stay after running the AC? Is 1-2 days normal?
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  15. #14
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    I wouldn't think so; no.

    Modern coils have a pretty close fin spacing - this is so they can have more surface area for heat exchange in a smaller physical space. So capillary attraction becomes a greater factor with higher efficiencies.

    The coil and the drain pan wants to first be Clean of everything. Residual oils, organics of every kind, as well as dust and dirt. And then it wants to be treated with a wetting-agent product - to promote 'sheeting' of the water rather than what might be called 'bunching' of the water.

    Is this a heat pump system? They have an additional problem in this regard.

    PHM
    --------
    I think this is only an air conditioner (evaporator coil in the attic, and condenser coil outside). Before the evaporator coil, there're a gas furnace for heating and a blower..

  16. #15
    Join Date
    Jan 2006
    Location
    In a land far, far away
    Posts
    17,477
    Post Likes
    Thanks, Mikey, I got tied up and couldn't respond.

  17. #16
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    I wouldn't think so; no.

    Modern coils have a pretty close fin spacing - this is so they can have more surface area for heat exchange in a smaller physical space. So capillary attraction becomes a greater factor with higher efficiencies.

    The coil and the drain pan wants to first be Clean of everything. Residual oils, organics of every kind, as well as dust and dirt. And then it wants to be treated with a wetting-agent product - to promote 'sheeting' of the water rather than what might be called 'bunching' of the water.

    Is this a heat pump system? They have an additional problem in this regard.

    PHM
    --------
    Sorry, but I just wanted to confirm, condensate water trapped for 1-2 days inside the evaporator coil after running AC isn't normal; instead, it should be dripping down to the pan and gone shortly after running AC?

  18. #17
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    38,065
    Post Likes
    Quote Originally Posted by greatman View Post
    Sorry, but I just wanted to confirm, condensate water trapped for 1-2 days inside the evaporator coil after running AC isn't normal; instead, it should be dripping down to the pan and gone shortly after running AC?
    after a day that water would be evaporated.

  19. #18
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Thanks to all for your help! Here's a quick update. I did the following in the last couple of days:

    1. steam clean the evaporator coil at a modest temperature. Just a simple handheld steam cleaner bought from Amazon.
    2. change the filter from MPR2200 to MPR1000
    3. use warm water mixed with a bit of dish detergent to clean the evaporator coil after steam cleaning

    The smell is unnoticeable now, and it's been more than a day! I can smell nothing from the vents when running fans; when the compressor is running, the air seems more humid than in the fan mode, but it doesn't smell musty (there's just some sort of humidity feeling)... I think it's just normal cold air. Keeping fingers crossed that the smell won't come back anytime soon!

  20. #19
    Poodle Head Mikey's Avatar
    Poodle Head Mikey is offline Membership Chair/ARP Committee / Professional Member*
    Join Date
    Sep 2002
    Posts
    33,087
    Post Likes
    Thanks. It's always nice to hear the Resssst of The Story.

    Take a look and verify that - after the cooling has been off for a few hours - that the cooling coil is not holding water in the fins.

    PHM
    -------

    ata
    Quote Originally Posted by greatman View Post
    Thanks to all for your help! Here's a quick update. I did the following in the last couple of days:

    1. steam clean the evaporator coil at a modest temperature. Just a simple handheld steam cleaner bought from Amazon.
    2. change the filter from MPR2200 to MPR1000
    3. use warm water mixed with a bit of dish detergent to clean the evaporator coil after steam cleaning

    The smell is unnoticeable now, and it's been more than a day! I can smell nothing from the vents when running fans; when the compressor is running, the air seems more humid than in the fan mode, but it doesn't smell musty (there's just some sort of humidity feeling)... I think it's just normal cold air. Keeping fingers crossed that the smell won't come back anytime soon!
    PHM
    --------
    The conventional view serves to protect us from the painful job of Thinking

  21. #20
    Join Date
    May 2022
    Posts
    11
    Post Likes
    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    Thanks. It's always nice to hear the Resssst of The Story.

    Take a look and verify that - after the cooling has been off for a few hours - that the cooling coil is not holding water in the fins.

    PHM
    -------

    ata
    Oh, yes, I'll check next week if condensate water is still being trapped in the fins after running AC. If water is still there, then the smell will come back soon..

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •