Why Does the Car AC Smell Bad?
A musty AC smell is common, usually caused by bacterial/fungal growth on the damp evaporator or a dirty cabin filter — and the fix is usually simple.
Causes
Moisture building up on the evaporator grows mold, a dirty/old cabin filter, or a blocked AC drain that pools water.
The fix
Start by replacing the cabin filter (cheapest and most effective), use a disinfectant spray for the evaporator/air ducts, and make sure the water drain is not blocked.
Prevention
Turn the A/C compressor off a few minutes before arriving while keeping the fan on to dry the evaporator, and change the cabin filter regularly. See the weak-AC-cooling guide for cooling issues.
FAQ
Smell stronger at first start?
Typical of evaporator mold — it fades after a few minutes. Disinfecting and a filter change fix it.
Is the smell harmful?
Fungal smells can bother sensitive or allergic people — best treated by cleaning the filter and evaporator.