How mold spreads through heating and air systems
Yes. Mold can grow inside air conditioning units, heating systems, and ductwork, where moisture from condensation collects. Because these systems push air through the whole home, mold in them can spread spores from room to room.
HVAC systems create the damp, dark conditions mold likes, especially when drainage is blocked or filters go unchanged for a long time. A musty smell that gets stronger when the heat or air conditioning turns on is a common warning sign. Since ducts carry air everywhere, mold there can affect the entire unit, not just one corner.
Maintaining shared building systems like central heating and air is generally the landlord's responsibility, so mold caused by a neglected HVAC system usually falls on them to address. If you notice a musty smell tied to your vents and your landlord will not have the system checked, keep notes and photos — and know that a free review can help you understand what the landlord is required to do.
This is general information about California tenant rights, not legal advice. Every situation is different.