Mildew odor from AC vents

[bdickson]

I'm getting a mildew/mold type odor from the ceiling AC vents when the units are running. There are no water leaks that I can find. Any suggestions for treatment? I was thinking of spraying some Clorox into the air return with the unit running. Bad idea or not?

[BFlinn181]

I'd check and see if the water that condenses on the rooftop coils is collecting in the pan under the evaporator. Perhaps the drain is blocked, allowing water to accumulate and get 'nasty.' Best to find the source of water rather than just treat the odor. If not a water issue in the pan, it could be moisture condensing on the ducting, which could be a mold issue.