OPTION: On air returns, it is possible to run the system blower fan, to help pull the mold remover deeper into the system. Just remember to turn the blower off before applying to an air register (which would blow the mold remover back at you)
3. Replace the vent cover
Apply the mold killer to the inside of the duct directing the spray as deeply as possible
Remove the air filter, and any other covers. Apply Mold Killer to all available surfaces.
Soak the outside coils with the MoldSTAT Plus mold remover.
Project wrap up
If the mold scent only comes from a couple vents, you could start by just treating those vents, and expand the project to the entire system if that doesn’t resolve the mold smell.
After DIY air duct mold removal if the mold problem doesn’t go away, you could either retreat or feel confident that the problem is truly larger than a DIY project, and hiring a air duct cleaning specialist is really necessary.