1. Check the Control Panel:
* Manual Controls: If you have manual climate controls, carefully inspect the controls themselves. Is the defrost setting stuck? Try repeatedly switching between defrost and other settings. Sometimes a stuck button or a loose connection within the control panel is the culprit.
* Automatic Controls (if equipped): If you have automatic climate control, the problem is likely more complex and may require professional attention. The system's computer might be malfunctioning.
2. Blend Door Actuator:
* Location: This is the most likely culprit. The blend door actuator is a small motor that controls the airflow direction. In a '96 Mustang, its location varies slightly depending on the specific model and whether you have AC or just heat. It is usually located behind the dashboard on the passenger side. Accessing it requires partial disassembly of the dashboard, which is a significant undertaking for a DIYer.
* Functionality: The actuator moves a blend door that directs air to the defrost vents, floor vents, or vents. If it's stuck in the defrost position, it won't allow the air to go anywhere else.
* Testing: This is challenging without removing the actuator. You *might* be able to hear a clicking sound from it if you turn the controls; however, you'll likely need to remove it to visually inspect it for binding or damage.
3. Wiring and Vacuum Lines (Less Likely):
* Wiring: A short circuit or a broken wire in the climate control system can cause the defrost to remain on. Tracing the wiring harness related to the climate control system is a complex and time-consuming task, best left to a professional unless you are very experienced.
* Vacuum Lines (Less common on '96 Mustangs, more likely on older models): Some older systems use vacuum lines to control the blend doors. If your Mustang uses vacuum control (unlikely), a leak in the line or a malfunctioning vacuum source could be the problem.
Recommendations:
* Start with the Simple Stuff: Begin by examining the control panel closely. Try cycling through the various settings multiple times.
* Consult a Repair Manual: A repair manual specific to your 1996 Ford Mustang will have diagrams and instructions showing the location of the blend door actuator and other components of the climate control system.
* Professional Help: Accessing and replacing the blend door actuator is often a difficult DIY job due to dashboard disassembly. Unless you're experienced with car repairs and have the right tools, it's usually best to take your Mustang to a qualified mechanic. The cost of repair is likely to be less than the cost and frustration of a botched DIY attempt.
Remember safety first when working on your car's electrical system. Disconnect the battery's negative terminal before working on any wiring.
