1. The Obvious Checks:
* Check the Child Safety Lock: Make absolutely sure the child safety lock (usually a small button or lever on the door edge near the handle) isn't engaged. This is the most common cause.
* Check the Interior Door Handle: Try opening the door from the inside. If it doesn't work from the inside, the problem is likely *not* with the exterior handle mechanism.
* Exterior Handle: If the interior handle works but the exterior doesn't, the problem is likely within the exterior handle assembly or its linkage.
2. If the Interior Handle Doesn't Work:
This indicates a problem deeper within the door mechanism. Here are potential causes and how to address them:
* Broken Cable: The interior door handle is typically connected to the latch mechanism by a cable. This cable can break, stretch, or become disconnected. You'll need to remove the interior door panel to access and inspect the cable. This is a moderately challenging task requiring some mechanical aptitude and the right tools (screwdrivers, possibly trim tools to avoid scratching the panel). Online repair manuals or videos for 1991 Ford Aerostar door panel removal will be essential. If the cable is broken, it will likely need replacing.
* Latch Mechanism Problem: The latch itself may be jammed, broken, or worn out. Again, you'll need to remove the interior door panel to access and inspect the latch. A jammed latch might be freed with lubricant (penetrating oil like PB Blaster), but a broken latch will require replacement.
* Rods and linkages: The interior handle connects to the latch mechanism through a series of rods and linkages. These can become disconnected, bent, or rusted. Inspect these carefully when you remove the door panel.
* Vacuum System (if equipped): Some Aerostars used a vacuum system to assist with door locking. If this system is malfunctioning, it could prevent the door from opening. Check the vacuum lines for leaks or blockages.
3. If the Interior Handle Works but the Exterior Handle Doesn't:
This suggests a problem with the exterior handle assembly or its linkage.
* Exterior Handle Mechanism: The exterior handle itself might be broken or jammed. Removing the interior door panel will give you better access to see if the exterior handle is properly connected to the internal mechanism.
* Broken or Disconnected Linkage: The linkage connecting the exterior handle to the latch mechanism could be broken or disconnected.
4. Tools and Resources:
* Repair Manual: A repair manual specific to your 1991 Ford Aerostar is invaluable. It will provide detailed diagrams and instructions for removing the door panel and accessing the internal mechanisms. You can often find these online (eBay, Amazon) or at auto parts stores.
* Screwdrivers (Phillips and flathead): You'll need these to remove the interior door panel.
* Panel Removal Tools (optional but recommended): These plastic tools help pry off the door panel without scratching it.
* Penetrating Oil (like PB Blaster): Useful for freeing up jammed or rusted parts.
* Replacement Parts: If you find a broken cable, latch, or linkage, you'll need replacement parts. Your local auto parts store or online retailers should be able to source these.
Important Safety Note: Before starting any repairs, disconnect the battery's negative terminal to prevent accidental electrical shocks or short circuits.
If you're not comfortable working on car doors yourself, take your Aerostar to a qualified mechanic. This repair can be more involved than it initially seems. Trying to force the door open could cause further damage.
