* Blend Door Actuator (Passenger Side): This is the most common cause. The blend door actuator is a small motor that controls the flow of hot and cold air to the vents. If it's malfunctioning or broken, it might be stuck in the "hot" position for the passenger side. This requires replacing the actuator itself.
* Blend Door Cable (If applicable): Some older systems use cables instead of actuators. A broken or dislodged cable on the passenger side would prevent cold air from reaching the vents.
* Vacuum Leaks (Less likely, but possible): Some climate control systems rely on vacuum to control blend doors. A leak in the vacuum lines could disrupt the system's ability to switch between hot and cold air on the passenger side. This is harder to diagnose and requires checking vacuum lines for damage or leaks.
* Wiring Issue (Least likely): A short or damaged wire specifically affecting the passenger side actuator's power supply is possible, but less probable than a mechanical problem with the actuator or cable.
* Stuck Blend Door (Rare): In rare cases, the blend door itself might be jammed or broken, preventing it from moving to the cold air position. This usually requires more extensive disassembly to access and repair/replace the blend door.
Troubleshooting Steps (in order of likelihood and ease):
1. Check the Controls: Make sure the temperature control for the passenger side is set to cold and the fan speed is sufficient. This sounds obvious, but it's a good first step.
2. Listen for the Actuator: When you switch the temperature control, you should hear a slight whirring sound as the actuator motor moves. If you don't hear it on the passenger side but do on the driver's side, the actuator is likely the culprit.
3. Visual Inspection (if possible): Access to the blend door actuators may vary by model year. If you're comfortable working on your car, you could try visually inspecting the actuator on the passenger side to see if it's obviously damaged or disconnected. (This often requires removing parts of the dashboard; not recommended for those unfamiliar with auto repair.)
4. Professional Diagnosis: If you're not comfortable tackling this yourself, take your Buick to a qualified mechanic or AC specialist. They have the tools and expertise to properly diagnose the issue. Mention the symptoms very clearly (only passenger side is blowing hot air).
It's crucial to have the issue diagnosed correctly. Simply replacing parts without a proper diagnosis could be expensive and unproductive. Start with the simplest checks and proceed from there.
