* Blend Door Actuator: This small motor controls the blend of hot and cold air going to each vent. If the passenger side actuator is malfunctioning or broken, it might not be able to properly direct cold air. This is the most likely culprit.
* Vacuum Leaks: The blend doors are often controlled by vacuum. A leak in the vacuum lines can prevent proper operation of the actuator, resulting in uneven temperature distribution. Check all vacuum lines connected to the HVAC system for cracks, holes, or loose connections.
* Blend Door Linkage: Less common, but the linkage connecting the actuator to the blend door itself could be broken or dislodged. This would prevent the actuator from effectively moving the blend door.
* Mode Door Actuator (Less Likely): While less likely to cause this specific symptom, a faulty mode door actuator could indirectly affect air distribution if it's malfunctioning and interfering with the blend door's operation.
Troubleshooting Steps:
1. Check the Vacuum Lines: Start by visually inspecting all vacuum lines related to the HVAC system. Look for cracks, holes, or loose connections. Repair or replace any damaged lines.
2. Listen for the Actuator: With the climate control system on, listen near the HVAC unit under the dash (you might need to remove some trim panels for better access). You should hear a clicking or whirring sound from the blend door actuators as they move. If you don't hear anything from the passenger side, it's a strong indicator of a faulty actuator.
3. Test the Actuator (Advanced): If you have a vacuum pump, you can directly test the passenger side blend door actuator. Disconnect the vacuum line and apply vacuum to see if it moves the blend door. This requires more mechanical aptitude and access to the actuator.
4. Replace the Actuator (Most Likely Solution): If the actuator is faulty, you'll likely need to replace it. This usually involves removing some trim pieces from the dashboard to access the actuator. You can find replacement actuators online or at an auto parts store.
Important Considerations:
* Safety First: Working on the dashboard can be tricky. Disconnect the battery negative terminal before starting any work to prevent accidental short circuits.
* Repair Manual: A repair manual specific to your 1995 Oldsmobile Ninety-Eight will be extremely helpful for accessing the HVAC system and identifying components.
* Professional Help: If you're not comfortable working on your car's HVAC system, it's best to take it to a qualified mechanic.
The blend door actuator is the most likely cause, but a thorough check of the vacuum system is crucial before replacing parts. Remember to consult a repair manual for detailed instructions specific to your vehicle.
