Here's a breakdown of why:
* Blend Doors: These are small flaps inside the heater core housing that regulate the mix of hot and cold air. A malfunctioning blend door (stuck, broken, or improperly operating) on the passenger side could be preventing cold air from reaching that side.
* Blend Door Actuator: This is a small motor that controls the position of the blend doors. If the actuator for the passenger side is faulty, it may not be able to correctly position the blend door to allow cold air to flow. This is a common failure point.
* Vacuum Lines: Some Saab models use vacuum lines to control the blend doors. A leak or blockage in these lines could affect the operation of the blend doors, leading to uneven temperature distribution.
* Heater Core: While less likely, a partially blocked heater core could also contribute, but this would usually manifest as reduced heat on *both* sides, not just one side being cold.
* Temperature Control Settings: Double-check that the passenger-side temperature control is actually set to cold and isn't accidentally set to a warm setting.
Troubleshooting Steps:
1. Check the temperature controls: Make sure the passenger side is indeed set to its coldest setting.
2. Listen for sounds: With the fan on, listen near the dashboard for any unusual clicking or whirring sounds, which could indicate a faulty actuator struggling to move the blend door.
3. Check vacuum lines (if applicable): Inspect the vacuum lines connected to the heater system for any leaks or damage.
4. Consult a repair manual: A repair manual specific to your Saab 9-3 model year will provide diagrams and detailed instructions for accessing and testing the blend door actuator and other components.
Repair: Usually, the solution involves replacing the faulty blend door actuator. This may require some mechanical skills and familiarity with car repair. If you're not comfortable working on your car yourself, it's best to take it to a qualified mechanic specializing in Saabs.
