The answer to 'why is my evaporator coil smells bad' is that a smelly evaporator coil is often caused by mold, mildew, or bacterial growth on the coil. This can happen when the coil gets too wet and doesn't dry out completely, creating a breeding ground for these microorganisms.
Some common symptoms of a smelly evaporator coil include a musty or moldy odor coming from the air vents, reduced airflow, and potentially even visible mold growth on the coil itself. In some cases, the smell may only be noticeable when the AC is running.