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Thread: smell coming from central air system

  1. #1
    Scientist jeremytl's Avatar
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    Default smell coming from central air system

    I remember this musty smell from when we lived in an apartment, years ago. Now I'm smelling it for the first time in 5 years.
    Its the same musty smell, I believe coming from the air ducts. We have a single story house with a crawl space. The air handler and propane furnace is under the house, in the crawlspace. This unit is 5 years old. The compressor unit sits outside the house on one side. The return takes a 24 x 12 x 1" filter and I change it about every 2 - 3 months. Again, We have lived here for 5 years and this is the first time we have smelled this.
    What should I check first?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    the evaporator coil may need cleaning as well as the drip pan under it. this is always wet, and any dirt that makes it past the filter will stick and become mold food.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Scientist jeremytl's Avatar
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    Quote Originally Posted by jadnashua View Post
    the evaporator coil may need cleaning as well as the drip pan under it. this is always wet, and any dirt that makes it past the filter will stick and become mold food.
    the coil and drip pan is located under the house or under the unit that sits outside?

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    DIY Junior Member Rat's Avatar
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    Under the house. You can try to clean the coil in place with a good cleaner or just water; but to get it really clean it needs to be pulled most likely. There are two products that will help once it is clean: BioGuard and BioFresh. Both will help keep the coil clean longer and if used a fog (with a fogger) will help keep ducts clean of Bio growth as well. There are many similar products and most of them I have tried work equally well. I use BioGuard and BioFresh because I like the way they smell better.
    There's nothing magical about it; it's all science, physics and math.

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    Scientist jeremytl's Avatar
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    thanks all.
    I'm going to have to google a diagram to look for the coils b/c I don't have the slightest idea of where to look or what it looks like.
    Can I assume these cleaners mentioned above can be found at any number of the big box hardware stores?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    There are two major parts to any a/c unit: the compressor (which has a bunch of heat exchanger coils...not the ones that need cleaning, although the thing does work better if they are kept clean) and the evaporator (the part that the air blows over). The evaporator is somewhere in your system...I think you mentioned an air handler - it's inside that. Underneath that is a drip pan, and there'll be a pipe coming out that drains the condensate away. So, look for the pipe that is draining and you'll be close.

    Think of stepping out of the pool on a windy day...the cooling effect you get is what's happening in your a/c unit, but it is the refrigerant that is evaporating. It gets pumped back to the compressor, where it extracts the heat and makes it liquid again, so it can all happen over and over again. Basically, an a/c is a heat pump that moves it from one place (in the house) to another (outside). That's why there's hot air coming out of the compressor system, and cold air coming out of the air ducts...the refrigerant moved it from one place to the other.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Scientist jeremytl's Avatar
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    very nice-
    thanks!

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