Where is the low charge nipple for AC system located on a 2001 Ford Expedition?

There isn't a "low charge nipple" in the way you might be thinking of on a 2001 Ford Expedition's AC system. Older vehicles, especially those without electronic climate controls, sometimes had service ports that looked like nipples. However, modern AC systems, including the one in your Expedition, use service ports with Schrader valves, similar to those on car tires.

You'll find these ports on the AC lines:

* Low-pressure side: This is usually a smaller diameter line and will be the port you use to check the low-side pressure. It's typically located near the compressor. It is often blue.

* High-pressure side: This is a thicker line and is used to check high-side pressure. It's usually located near the condenser. It's often red.

To find them, you'll need to visually inspect the AC lines under the hood of your Expedition. Look carefully near the compressor and condenser. The ports will be capped, but you'll see them easily enough. They'll likely be capped with small dust covers.

Warning: Working with automotive AC systems involves refrigerant that is under pressure and can cause serious injury. If you're not experienced with AC system service, it's strongly recommended to take your vehicle to a qualified mechanic for any AC repairs or recharge. Improper handling of refrigerant can be dangerous and illegal.