Mold in Air Conditioning Units: How to get rid of mold in your air conditioning unit

Money Pit Team asks,

My son lives in an apartment complex that houses mostly college students. Since he moved in, he has been sick almost constantly with lung issues up to and including coughing up blood. We recently found that the air conditioning and heating unit in his apartment is covered in mold and mildew on the inside. Although they have come out and cleaned the unit, I think they need to do more than just cleaning the coils. Is that enough to get rid of the mold or are they just shoveling sand against the tide if they don’t treat the ductwork as well as the rest of the apartment?

Our Answer

Mold spores tend to gravitate toward places that are moist and have air and organic matter to serve as food. This combination of conditions can be found everywhere from furnishings to cardboard boxes, but as you and your son have unfortunately discovered, one of the biggest and most often overlooked homes for mold is the air conditioner.
Whether a portable or part of a central air setup, an air conditioner’s coil and everything around it is damp while the machine runs, which attracts mold. Without adequate filtration, mold is bound to grow.
Using a decent filter can make all the difference─that means a pleated filter with a MERV (Minimum Efficiency Reporting Value) rating of at least 8, or 11 in the home of someone prone to allergies. If the air conditioner in your son’s apartment is a wall unit, its original filter would’ve had a MERV rating far lower than 8, so an immediate filter upgrade is in order.
Considering your son’s serious condition though, the best advice would be for him to move out. There’s no sense staying there if it is making him sick. Mold effects different people in different ways and if he is that sick, he needs immediate medical attention and a clean, mold-free place to live as soon as possible.