We would like to find the cause and not spend lots of money on a band aid that may not work. Id call the duct cleaning company back and have them clean the duct again!They should have cleaned the duct and the AHU the first time.It eventually died down in several days, but still had nasty dank odor when A/C would kick off.We run our fan continually to filter the air so we would really notice it when the cool shut off. Has always had slight dusty dirty odor from vents and A/C was smelly when it kicked off, but not as bad as this year.
Believe it or not I just came from my parents home and when I walked in they had a very strong musty odor which was coming from there basement because it is alittle damp but they had a small cold air return which was sucking in the odor from there basement and spreading it thru out there home, so I closed it off and turn the fan on high for about a hour and opened a few doors and windows and the smell was soon gone. If you do close it off and see what happens after a hour or so with the fan on high and fresh air allowed to circulate thru out the home and see it that helps with the odor your claiming your home has. These lights are very powerful ultra violet radiation lights that kill dust mites bacteria and mold.
Called the environmental company again who sent out a team to do a recovery level fogging of the duct system.
They noticed a smell that settles in ducts when furnaces have been run with burning dust and debris on them.
Have been dealing with layers of odor from HVAC system for the last 3-4 months.
When we started up A/C in May it had a dirty maple-brown sugar smell.
Maybe you can get some money back since they did not clean the AHU.