The answer to 'AC smells bad' is that a smelly air conditioner is often caused by mold, mildew, or bacterial growth in the system. This can happen when moisture builds up in the unit, often due to poor drainage or lack of maintenance. The smell may be musty, rotten, or unpleasant.
Some common symptoms include a foul odor coming from the vents, visible mold growth in the unit, and even potential health issues like allergies or respiratory problems for those in the home. To fix the problem, you'll need to clean and disinfect the AC system, which may require professional HVAC service in some cases.