HVAC Dirty Sock Syndrome

[Alex Svet]

Hey everyone. I'm hoping to get some advice/info related to the issue I'm having. Perhaps there were folks that experienced similar in the past, and hopefully were able to get it fixed.

I have a 2.200sc f townhouse built in 1999 with an 7-8 year old HVAC. The issue is with the AC system, when it's in the AC mode the house is being filled with bad odor that is coming from the vents. The contractor that we've been working for month has had AC coil replaced to a new one as well as organic chemicals sprayed into the system, the procedure was performed three times and helped for a short period of time.

The issue that is being described here is also known as "dirty sock syndrome". 99% of the time it's getting solved with coil replacement. This unfortunately did not work with our house and we are at the moment discussing next steps. The contractor suggests duct cleaning that we'll do anyway, but I was wondering if anyone has had a similar issue like ours and could provide additional info on the questions below:

- some additional info re reason of the smell (what kind of bacteria is it?)

- what are other reasons that might cause the smell

- what are the other measures someone might have taken to prevent it from happening again besides coil replacement, etc.

The contractors I have talked all suggest that issue always fixed with coil replacement. But are clueless to what could be the reason besides the coil.

Thank you in advance,

Alex