The answer to 'air handler smells bad' is that there are several common causes, including mold, mildew, or bacterial growth in the unit. Symptoms may include a musty or unpleasant odor coming from the air vents or air handler itself. Addressing the issue promptly is important, as it can indicate a more serious problem that requires professional attention.
Some potential solutions for a smelly air handler include thoroughly cleaning the unit, replacing the air filter, and addressing any moisture or humidity issues in the home. However, if the odor persists or you suspect mold or other contaminants, it's best to call in a professional HVAC technician to diagnose and resolve the problem safely.