I have to agree with El that mold in the evaporator can be a problem, especially in humid environments. One of the other problems is that your home AC recirculates the same air repeatedly. Some people think this can allow the air to get "stale." Perhaps it does. One thing I've noticed is that many homes don't have filters on their AC return ducts. This is bad for the system because it can allow the evaporator to become clogged with dust, cat hair, and any solid material light enough to float in the air long enough to get sucked in. The shit that passes through the evaporator winds right back up in the air you're breathing.
On the homes that do have filters in place, many of them use the cheapest filters they can find. The really cheap filters may only be good for removing large particulate like cat hair. About the only advantage to using them is they don't restrict airflow. On the opposite end of the spectrum you have the 3M Filtrete filters in the black packaging which trap damn near everything. Your evaporator needs to be spotless as they will reduce your airflow a bit, and any shit on the evaporator will reduce it more. But if you've got problems with allergies, airborne mold, dust, and pet dander, they're the best you can get in a disposable filter. They are pricey and need replacement about every 6-8 weeks.
But if you use the AC and wake up feeling congested or just shitty, switch to a better filter. The 3M that costs $20 takes out a lot more shit than the generic that costs $2.
On the homes that do have filters in place, many of them use the cheapest filters they can find. The really cheap filters may only be good for removing large particulate like cat hair. About the only advantage to using them is they don't restrict airflow. On the opposite end of the spectrum you have the 3M Filtrete filters in the black packaging which trap damn near everything. Your evaporator needs to be spotless as they will reduce your airflow a bit, and any shit on the evaporator will reduce it more. But if you've got problems with allergies, airborne mold, dust, and pet dander, they're the best you can get in a disposable filter. They are pricey and need replacement about every 6-8 weeks.
But if you use the AC and wake up feeling congested or just shitty, switch to a better filter. The 3M that costs $20 takes out a lot more shit than the generic that costs $2.