Help! Strong Musty Garbage Smell When A/C Comes On

Problems related to residential installations.

Help! Strong Musty Garbage Smell When A/C Comes On

Postby sarasota » Sat Jan 08, 2011 1:50 pm

Hello all,

The other day, I turned on my central air for the first time in two months and I immediately noticed an overwhelming odor that smelled like musty garbage. I had been using my central heating for two months prior to this and never smelled this odor. Nor did I smell it last summer when I was constantly running the a/c. When I have been running the heat or fan only, I do not smell the odor. It only starts when the a/c is switched on. I live in the Florida area.

I had a tech check the evaporator coils and from the front view, they appeared clean and mold/gunk-free. The drip pan was dry but he did notice a generous collection of an oily type substance in the corner of the pan. He said it had an odd smell and then cleaned it up. He checked the attic for the odor had described and carefully inspected the duct work. He didn't find anything unusual and suggested that maybe I should get the ducts cleaned...

The A/C unit is about 7 years old and in excellent shape I've been told. The coils have some rust on them however. The A/C system is very efficient so I do not believe that I have a Freon leak. I also have the unit maintained regularly. Because the odor is not present when the fan only or heat have been running, I don't believe that it is a problem with mold or dust in the ducts. The air handler is located in the garage. The garage area is odor-free. I had the attic inspected for rodents and nothing was found.

So, I am at a complete loss. Other than having the evaporator coil unit pulled and cleaned, does anyone have any other theories on what might be going on here? I am scared to use the A/C now...

Thank you so much!

Stinky in Sarasota
sarasota
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby juster » Sat Jan 08, 2011 6:35 pm

Did your tech leak test the coil. Oil can migrate with refrigerant. A very small leak will leave a trace of oil at times. The unit could run for some time if the leak is small without you noticing a problem with it. With a small refrigerant leak you may not actually smell anything. Not 100% sure this is the problem. Kinda funny the smell only there when the AC is running and not the fan or heat.
If the tech did not do a refrigerant leak test, you may want to have them do one. This test involves the tech using a very sensitive refrigerant sensor to detect any leak. They can also use a soap solution but unless you have access to the evaporator coil (some are hard to get to) the sensor is the other method.
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby nomadpeo » Sun Jan 16, 2011 4:01 pm

dear stinky (lol) - it is a strange problem. a pungent odor can come from refrigerant oil. a small amout circulates in the evaporator coil while the ac is running and returns to the compressor. if there is a leak, it could potentially accumulate in the drain pan and the smell of it passed in the air. grasping for straws here, because it does not really seem like a good theory for your problem. as far as the performance of your system being affected by a small leak, you may not be able to detect the problem yet in terms of effieciency until it leaks more, but a proper check of the freon level and a eld (electronic leak detector), as mentioned, could rule that out.

i would more tend to think it has to do with some growth, such as mold or algae on the coil. i know you said it was checked, but we all miss something from time to time. i would revisit the issue. since it only happens when freon is flowing, logic would dictate that conditions are condusive for some combination of moisture, temperature and humidity to generate the growth of a mold, algae or something causing the smell. if this is so, you are lucky enough to detect it. your tech may need to bring in another set of eyes and take a closer look at the situation. some of these conditions can cause real problems. at the very least, there could be a dead critter in the back corner of the pan that generates a smell when the pan has water it it.

the only other wild theory i can come up with that matches coincidence of ac running is maybe a slow burning wire or component. i would think a tech would pick up on that if it was the case........again, grasping at straws.

i would certainly be interested in knowing what it was when you find out. good luck.
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby sarasota » Mon Jan 24, 2011 4:06 pm

Firstly, thank you to nomadpeo and juster for your input.

Had a technician come out from another company to diagnose the problem. After checking everything, he was 99% convinced that the foul odor when running the a/c was due to a microscopic mold build-up on the evap coils (invisible to the human eye). Although the the coils appeared clean, there was likely something going on behind the scenes as nomadpeo had suggested. No leaks were detected in the coils which was great news. The tech thoroughly cleaned and then sanitized the coils with a special chemical which kills mold and bacteria and flushed the drain pipe. I also purchased and installed a brand new filter in case some mold spores were hanging around on the old one.

Finally, I tested the a/c and magically, the foul order had disappeared and has not returned since.

Thank you so much for everyone's input. It gave me something to go on. Otherwise, I would've ended up having all the ducts cleaned as suggested by our original a/c tech, etc., etc. resulting in a huge expense.
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby sarasota » Thu Feb 17, 2011 8:14 am

Well, unfortunately the musty smell is back after only one month... I am at a loss. Other than getting the coils cleaned every month which can get costly, I'm not sure what else to do other than have a UV light installed which I am somewhat against doing. Any ideas?
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby nomadpeo » Thu Feb 17, 2011 8:32 am

what is your apprehension about a uv light. the technology is proven to be effective and safe. there are a variety of products designed to be installed to expose your evaporator coil. do some research on that subject and call a company in your area that speacializes in INDOOR AIR QUALITY. IAQ is a responsibility of all of us who service these systems, but you may need a specialist to verify through testing what, if anything is growing, then investigate possible design/service issues contributing to conditions condusive to that growth. good luck.
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby sarasota » Sat Feb 19, 2011 9:49 pm

Thanks so much for your input nomadpeo. I was confusing the UV light with the ozone system that our a/c tech is trying to get us to install. We agreed to start with the UV light to see if that solves the issue. We are having it installed tomorrow. I am also going to look into hiring an IAQ specialist. Perhaps they could shed some light on things. Failing that, we may consider having a brand new evap coil installed $$$$$. The newer ones are supposed to deter mold/fungus growth.
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- Help! Strong Musty Garbage Smell When A/C Comes On

Postby nomadpeo » Mon Feb 21, 2011 12:09 am

research and consult with multiple contractors before buying. not even the best machines can overcome some problems with a poor design and installation.

let us know how the uv works out for you.
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