* Blocked Air Filter: This is the most common cause. A severely clogged air filter restricts airflow completely. Locate the air filter (usually under the hood or sometimes inside the passenger compartment) and replace it with a new one.
* Vacuum Leaks: The system uses vacuum to control the air direction (dash vents, floor vents, defrost). A leak in the vacuum lines can prevent proper operation of the vents. Inspect the vacuum lines for cracks, disconnections, or damage.
* Blend Door Actuator Problems: These small motors control the direction of the airflow (e.g., to the face, feet, or windshield). A malfunctioning actuator can prevent air from reaching the vents. These can be difficult to diagnose and may require specialized tools or replacement.
* Mode Door Problems: Similar to blend door actuators, but these control the overall mode of airflow (e.g., vents, floor, defrost). A stuck or broken mode door can prevent air from reaching the desired location.
* Plugged Ducts: Over time, debris can clog the air ducts themselves, restricting or blocking airflow. This is less common but possible, especially if the car has significant age or has been exposed to dust or debris.
* Faulty Blower Motor Resistor: While you say the blower motor *works*, a faulty resistor could be limiting the airflow to an undetectable level. This is less likely if you can hear the fan running strongly.
Troubleshooting Steps:
1. Check the air filter: This is the easiest and quickest check. Replace it if necessary.
2. Listen carefully: Does the fan sound normal? Does it change speed correctly? A weak or unusual sound might indicate a problem with the blower motor or resistor.
3. Check all vents: Are *all* vents blocked, or just some? This can help pinpoint the problem area (e.g., a problem with a specific actuator or duct).
4. Inspect vacuum lines: Look for any visible damage or disconnections.
5. Check the blower motor resistor: Accessing this may require some disassembly, depending on your car's model.
If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. Describing the symptoms clearly (blower fan runs, but no air from vents) will help them quickly identify the likely cause.
