The answer to 'evaporator coil smells bad' is that a bad odor coming from the evaporator coil is often caused by mold, mildew, or bacterial growth. This can happen when the coil gets wet and doesn't dry properly, creating a damp environment that allows microorganisms to thrive.
Some common symptoms of a smelly evaporator coil include a musty or rotten odor coming from the vents, poor airflow, and potentially even visible mold growth on the coil. The solution typically involves cleaning the coil thoroughly to remove any built-up grime and kill the mold or bacteria. This is a task that can be done DIY, but may require professional HVAC service if the problem is severe or difficult to access.