1. Verify the Problem:
* Is the rear AC *completely* inoperative? Sometimes a different issue (like a blown fuse, refrigerant leak, or failed compressor clutch) can mimic a vacuum problem. Rule out these other possibilities first. Check fuses related to the AC system.
* Listen for the rear AC actuator motor. When you turn on the rear AC, can you hear *any* sound from the actuator motor (located near the rear HVAC controls)? Silence suggests a potential electrical or vacuum problem.
* Check the rear AC controls. Ensure the controls are correctly set to activate the rear AC.
2. Locate the Vacuum Source and Lines:
* Vacuum Reservoir/Pump: The Windstar's vacuum system likely uses a vacuum reservoir (sometimes called a vacuum canister or pump) to store and distribute vacuum. This is typically located under the hood. Find its location in your vehicle's repair manual.
* Vacuum Lines: Trace the vacuum line(s) from the vacuum reservoir to the rear of the vehicle. Inspect them carefully for cracks, leaks, disconnections, or kinks. Pay close attention to the line(s) specifically going to the rear AC actuator. Look for obvious visual damage.
* Vacuum Switch/Solenoid (if applicable): Some systems use a vacuum switch or solenoid to control vacuum flow to the rear AC actuator. This is less common but possible.
3. Test for Vacuum:
* Use a Vacuum Gauge: This is the most reliable method. Connect a vacuum gauge to the vacuum line at various points, starting at the reservoir and working your way back to the rear AC actuator. This will tell you where the vacuum is lost. A proper vacuum reading should be around 18-22 inches of mercury (inHg). A low reading indicates a leak.
* Listen for hissing: With the vacuum system running (engine running), carefully listen along the vacuum lines for any hissing sounds indicating a leak.
4. Possible Causes and Solutions:
* Leaking Vacuum Line: Repair or replace any damaged or leaking vacuum lines.
* Clogged Vacuum Line: If you suspect a clog, try using compressed air (carefully!) to clear the line. Be cautious not to damage the line.
* Failed Vacuum Reservoir/Pump: If the reservoir isn't building sufficient vacuum, it may need to be replaced.
* Vacuum Solenoid/Switch Failure (if applicable): Test the solenoid/switch for proper operation. This might require a multimeter.
* Rear AC Actuator Motor Failure: A faulty actuator motor may not be able to respond to vacuum, even if it's present. You can test this by applying vacuum directly to the actuator (if you're comfortable doing so and have the necessary equipment).
* Loose or disconnected vacuum lines: This is a common and easily overlooked problem.
5. Use a Repair Manual:
A Ford Windstar repair manual specific to your year is invaluable. It will provide diagrams of the vacuum system, component locations, troubleshooting steps, and wiring diagrams. You can find these online or at auto parts stores.
Important Considerations:
* Safety First: Always disconnect the battery's negative terminal before working on electrical components.
* Vacuum System Pressure: Be cautious when working with the vacuum system. While not dangerous in the same way as high-pressure systems, improperly handling vacuum lines can lead to leaks and further issues.
* Refrigerant: Working with the A/C system involves refrigerant. Improper handling can be harmful. If you suspect a refrigerant leak, it's best to have a professional handle it.
If you're not comfortable working on your vehicle's vacuum system, it's advisable to take it to a qualified mechanic for diagnosis and repair. Improper repairs can lead to further damage.
