* Blend Door Actuators: These small motors control the direction of airflow (defrost, floor, vents, etc.). If one or more are malfunctioning, they might be stuck in a position that forces air to the floor and defrost vents, regardless of your selection. This is the most common cause. They can fail mechanically (gears stripping) or electrically (motor burning out).
* Mode Door Actuator: This is specifically responsible for selecting between defrost, floor, and vents. A faulty mode door actuator can lead to the issue you are describing.
* Climate Control Module (CCM): This is the "brain" of the system. It receives your input (button presses) and sends signals to the actuators. A faulty CCM can misinterpret your commands, leading to incorrect airflow.
* Vacuum Leaks (Less Likely on this model): Older vehicles sometimes use vacuum lines to control the blend doors. While less common on a 2007 Impala (which is more likely electronically controlled), a significant leak could disrupt the airflow. However, if it were a vacuum leak, you'd likely see inconsistent behavior in other areas of the system as well.
* Wiring Issues: A short circuit or broken wire in the system's wiring harness can prevent proper signals from reaching the actuators.
Troubleshooting Steps (in order of likelyhood and ease):
1. Check the Climate Control Settings Carefully: Double-check *everything*. Make sure you haven't accidentally engaged a "max defrost" or similar setting.
2. Listen Carefully: When you change the vent settings, do you hear any unusual clicking or grinding noises coming from behind the dashboard? This could indicate a struggling blend door actuator.
3. Diagnose with a Scan Tool (Best Approach): A scan tool capable of reading HVAC codes can pinpoint the faulty component. Auto parts stores often offer free code reading. This will be the most efficient way to find the problem.
4. Visual Inspection (Difficult): Accessing the actuators usually requires partial dashboard disassembly. This is best left to a mechanic unless you are very comfortable working on cars. Inspecting for visible damage to wiring is also a possibility.
What to Do:
* Start with the scan tool: This will save you time and money.
* If a scan tool identifies a faulty actuator: Replacing the actuator is relatively straightforward, though it may require some mechanical skill.
* If the CCM is the culprit: Replacement is more complex and generally more expensive.
Unless you're experienced with automotive repair, taking your 2007 Chevy Impala to a mechanic or an experienced auto technician is recommended. They have the tools and expertise to diagnose and fix the problem efficiently.
