1. Check the Actuator (Most Likely Culprit):
* Location: The blend door actuator responsible for windshield/floor/vent direction is usually located behind the dashboard, near the heater core. Accessing it requires some disassembly. Consult a repair manual (Haynes or Chilton) specific to your 1999 Windstar LX to find the exact location and proper disassembly procedure. This is *not* a simple job.
* Inspection: Once you access it, visually inspect the actuator. Look for:
* Broken linkage: The plastic linkage connecting the actuator motor to the blend door might be broken or dislodged.
* Seized motor: The motor itself might be seized due to age or lack of lubrication. Try gently turning the actuator shaft by hand. If it's stiff or doesn't move freely, it's likely the culprit.
* Wiring issues: Check the wiring harness connected to the actuator for any loose, broken, or corroded wires.
* Testing (If Possible): If you can safely access the actuator's electrical connector, you *might* be able to test it with a multimeter (check for voltage when the selector is moved). However, this is advanced troubleshooting and should only be attempted if you are comfortable working with car electronics.
2. Check the Control Module (Less Likely):
The blend door actuator is controlled by a module (often part of a larger climate control unit). A faulty module can prevent the actuator from receiving the correct signals. However, this is less likely than a faulty actuator itself. Replacing the entire control module is expensive and complex.
3. Vacuum System (Older Vehicles):
While less common in 1999 models, some vehicles used vacuum systems to control the blend doors. If this is the case (check your repair manual), check for leaks in the vacuum lines.
4. Repair Options:
* Replace the Actuator: This is usually the most effective solution if the actuator is faulty. You'll need to purchase a replacement actuator specific to your 1999 Windstar LX.
* Lubricate the Actuator (If Seized): If the motor is just seized, carefully lubricating it with a suitable lubricant might restore its function, but this is a temporary fix and won't address any internal mechanical issues.
* Repair Linkage: If the linkage is broken, you might be able to repair it with careful use of glue or by replacing the broken part.
Important Considerations:
* Repair Manual: A repair manual specific to your vehicle is crucial for safe and effective repair. It will provide detailed instructions on accessing the actuator, removing components, and reinstalling them.
* Safety: Disassembling parts of the dashboard is complex. If you're not comfortable with automotive repair, it's best to take your vehicle to a qualified mechanic. Improper disassembly can lead to damage to other components.
In short, while it *could* be a wiring or control module issue, the most probable cause is a malfunctioning blend door actuator. Start by accessing the actuator and visually inspecting it. If you are not confident performing this repair yourself, it is strongly recommended to take it to a professional.
