1. Listen and Observe:
* Listen for the compressor running: When you turn the key to the "on" position, but not start the engine, you should hear the compressor cycle on for a brief period. If you don't hear anything, it's a strong indicator the compressor isn't engaging.
* Check for leaks: With the engine off, visually inspect the air lines and suspension struts for any visible leaks. You might see small bubbles coming out of the air lines or a hissing sound.
* Check for air pressure: The air pressure in the struts should be around 75-100 PSI. Use a tire pressure gauge to measure the pressure in each strut. If the pressure is low or inconsistent, it might be a sign of a bad compressor or a leak in the system.
2. Electrical Testing:
* Check for power at the compressor: With the key in the "on" position, use a multimeter to test for voltage at the compressor's electrical connector. If there's no voltage, the compressor isn't receiving power, which could be due to a wiring issue or a problem with the control module.
* Test the compressor's relay: The compressor relay is responsible for sending power to the compressor. If the compressor is not getting power, you can test the relay by swapping it with a known good relay from a different system.
3. Visual Inspection:
* Look for signs of damage: Examine the compressor itself for any signs of damage, such as cracks, rust, or burnt wiring. If you see any damage, it's likely the compressor needs replacement.
4. Get It Checked:
* Take it to a mechanic: If you're not comfortable diagnosing the issue yourself, the best course of action is to take your Expedition to a mechanic. They have the tools and expertise to properly test the compressor and identify the problem.
Troubleshooting Tips:
* Use a reliable repair manual: A repair manual specific to your 1998 Ford Expedition will provide detailed wiring diagrams and troubleshooting steps.
* Be careful with electricity: Always disconnect the battery before working on electrical components.
* Safety first: If you're unsure about any steps, it's better to err on the side of caution and consult a professional.
By following these steps, you can narrow down the cause of the problem and determine if the suspension compressor is faulty. Remember, this is just a guide, and you should always consult a professional mechanic for a definitive diagnosis and repair.
