* Blend Door Actuator: This small motor controls the direction of the air (vent, defrost, floor). If it fails, it can get stuck, causing air to flow in an unintended direction. The malfunction could be mechanical (broken gear, stripped teeth) or electrical (faulty motor, wiring). The check engine light might be triggered because the system is reporting a malfunction to the onboard computer.
* Vacuum System (Less Likely but Possible): Older vehicles sometimes use vacuum lines to control the blend doors. A leak in these lines could disrupt proper airflow. This is less likely given the check engine light.
* Wiring/Electrical Problems: A short circuit or damaged wiring to the blend door actuator or other climate control components could cause erratic behavior and trigger the check engine light.
* Climate Control Module (Rare but possible): The main climate control module itself could be failing. This is less probable than the blend door actuator but worth considering if other checks don't reveal the problem.
* Refrigerant Issues (Less Likely): While fogging windows is usually related to the HVAC system, it's less likely to directly cause the air vent issue, and the check engine light usually isn't involved in simple refrigerant leaks.
Troubleshooting Steps:
1. Check the Check Engine Light: Use an OBD-II code reader to get the diagnostic trouble code (DTC). This code will give you a clue as to the specific problem the computer has detected.
2. Listen Carefully: With the car running, listen near the dashboard area while you switch between vent and defrost. You might hear a clicking or grinding sound coming from the blend door actuator if it's malfunctioning.
3. Visual Inspection (Advanced): If you're comfortable working on your car, you can access the blend door actuator (location varies by model, so you'll need to consult a repair manual). Look for any obvious signs of damage, such as broken wires or a seized motor. *Caution*: Working on the dashboard requires care to avoid damage.
Recommendation:
Unless you have experience working on car HVAC systems, it's best to take your Buick to a qualified mechanic or auto repair shop. Diagnosing and fixing the problem yourself might be difficult, and you risk causing more damage. The diagnostic trouble code from the check engine light will be very helpful to them.
