Here's a breakdown of why this happens and what you can do:
* Faulty Blend Door Actuator: The most likely culprit. Over time, these actuators can wear out, seize up, or break, preventing them from properly mixing the air.
* Vacuum Leak: The blend doors in some vehicles are controlled by vacuum. A leak in the vacuum lines can prevent proper operation of the doors.
* Blend Door Linkage Problem: The actuator might be working, but a broken or disconnected linkage could prevent the blend door from moving correctly.
* Wiring Issues (less likely): While less common, a problem with the wiring to the actuator could also cause this.
What you can do:
1. Check the HVAC Controls: Make sure the temperature controls are set correctly. Sometimes, it's a simple user error!
2. Listen for the Actuator: When you change the temperature settings, listen carefully near the dashboard. You should hear a small motor whirring as the actuator moves. If you hear nothing on the passenger side, that's a strong indicator of a failed actuator.
3. Inspect Vacuum Lines (if applicable): Check the vacuum lines related to your HVAC system for cracks, leaks, or disconnections. Repair or replace as needed. This is more likely if you have similar issues with other functions controlled by vacuum.
4. Visual Inspection (difficult): Accessing the blend door actuator often requires partial dashboard disassembly. If you're comfortable with auto repair and have the tools, you could try to visually inspect the actuator and linkage for damage. It's usually located behind the glove box or under the dash.
5. Replacement: If the actuator is faulty, you'll need to replace it. This is often the most cost-effective solution. You can find replacement actuators online or at auto parts stores. Be prepared for some disassembly of the dashboard to reach it.
Recommendation: Unless you're experienced with auto repair, it's generally best to take your Grand Prix to a qualified mechanic. They'll be able to diagnose the problem accurately and perform the necessary repair or replacement. The cost of a professional repair will likely be less than the cost of buying the wrong parts and potentially causing further damage.
