Open your air vents using a screwdriver. Shine a flashlight and look for visible signs of mold inside the vents. If you have any leaks or water damage, mold may accumulate in that particular area. Mold will appear moist and thick. You should also notice a musty aroma.
Open your central AC unit and remove the filter (wear rubber gloves if you suspect mold). Examine the filter carefully for visible signs of mold. Dirty air filters will frequently develop mold, since dirt and moisture both collect on the porous surface. When mold accumulates on filters, the spores can easily travel into the vents when you run the unit.
Observe the color and consistency of any mold you find. Molds appear in different colors with different consistencies, but black mold is thick and slimy. While it does look primarily black, it also has traces of dark green pigmentation.
Turn on your central air conditioning unit briefly and observe any musty odors that emerge through the air vents. If a mold colony is too deep within the unit for you to physically see, you may still smell it as the air pushes the aroma through the system. Do not leave the air on for more than a minute or two if you suspect black mold. Over time, the spores may spread through your home.
Call a mold remediator immediately if you see or suspect black mold inside your unit. A mold expert can sample the spores and verify that you have mold growing in the first place (only a proper analysis can make an exact determination). If you do have mold (even black and green mold), it may turn out to be a less harmful strain than Stachybotrys.