This video shows how to remove/replace the inside cabin air filter, and where to spray disinfectant to improve the problem. The inside filter is supposed to keep the air coming in through the vents dust free. In humid weather it can get wet and mildew causing it to smell very bad. I've battled the smell during the very hot humid times of summer, but the filter has always been dry when I check it and didn't have any mold built up. The odor will come out of the air conditioning vents. The problem happens during hot humid weather when the air conditioning holds moisture and gets a mildew or sweaty socks odor. This can be caused by a clogged air conditioner drain. It will accumulate dirt, leaf particles and such which can turn into a kind of mud inside the drain pan and clog the drain. If this is clogged, you may need to have a mechanic put the car on a lift to get under it and clean out via the drain tube.
