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!
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!
source https://hvac-talk.com/vbb/threads/2238681-Musty-smells-from-the-vents?goto=newpost
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