* Rear Blend Door Actuator: This is the most probable cause. The blend door actuator controls the flow of air between hot and cold in the rear. If it's malfunctioning or stuck, it might not be allowing cold air to reach the rear vents. It's a relatively common failure point in vehicles with separate rear climate control.
* Rear Evaporator Core (less likely): While less likely than the blend door actuator, it's possible the rear evaporator core (the part that cools the air) is clogged, restricted, or has a leak. This is less probable since the front works, but it's still a possibility.
* Rear Blower Motor/Fan (less likely): If the rear blower motor isn't working, you won't get any air at all, regardless of temperature. This is less likely given you're stating there's air, just not cold air. However, a weak blower motor could be struggling to move sufficient air through a restricted system.
* Clogged or Restricted Vents: Check the rear vents themselves to make sure they're not blocked by debris. While unlikely to be the sole cause, it could exacerbate a minor problem elsewhere.
* Wiring or Vacuum Line Issues: Problems with the wiring to the rear actuator or a vacuum line (if the system uses vacuum) could prevent the actuator from working correctly.
Troubleshooting Steps:
1. Check the Rear Vents: Ensure nothing is blocking the vents.
2. Listen Carefully: When you turn on the AC, listen near the rear vents. Do you hear any clicking or whirring sounds that might indicate the blend door actuator is trying to move? The absence of such sounds suggests a problem with the actuator.
3. Check the Rear Blower Speed: Is the blower motor actually running in the rear? If not, that's a separate problem (blown fuse, bad motor, etc.).
4. Access the Rear Actuator (if comfortable): This often requires some disassembly, and may be difficult. You'll need a repair manual or online guide specific to your vehicle's year and model to safely access it. Inspect the actuator for any obvious problems.
Recommendation:
Unless you're comfortable working on car AC systems (which can contain refrigerants requiring special handling), it's best to take your Oldsmobile Silhouette to a qualified mechanic or auto AC specialist. They have the tools and experience to diagnose and repair the problem efficiently. The blend door actuator is usually a relatively inexpensive and straightforward repair for a professional.
