Here's why:
* Leaking engine oil/coolant: The most likely cause is a significant engine problem. Burning oil (blueish-gray smoke) or coolant (white smoke) is being drawn into the HVAC system through various pathways. These could include:
* Leaking seals around the engine: Worn seals can allow oil or coolant to leak onto hot engine parts, causing it to burn and create smoke.
* Cracked engine block or head gasket: A serious engine problem resulting in a mix of oil, coolant and combustion byproducts being pushed into the air intake.
* Crankcase ventilation system issues: The PCV (Positive Crankcase Ventilation) system can malfunction, allowing oil vapors to escape and be drawn into the intake.
* Air intake location: The air intake for your car's HVAC system is often located near the engine. If smoke is present around the engine, it will be readily drawn into the ventilation system, particularly if the heater is on or the AC is on recirculate.
In short: The AC system isn't producing the smoke. It's simply acting as a conduit for smoke that's already being generated by a serious engine problem. You need to immediately address the underlying engine issue. Ignoring this could cause catastrophic engine damage. Take your car to a mechanic for diagnosis and repair as soon as possible.
