Other less likely possibilities include:
* Wiring issues: A short, break, or corroded connection in the wiring harness leading to the blower motor or resistor pack.
* Blower motor itself: Though less common, the motor could be failing and only functioning at its maximum speed.
* Switch problems: Though rare, the blower motor switch itself could be faulty.
Troubleshooting steps:
1. Check the resistor pack: This is the most likely culprit. Locate the resistor pack (usually under the dash, near the blower motor). Inspect it visually for any signs of burning, melting, or damage. A simple multimeter test can confirm whether it's functioning correctly. Replacing the resistor pack is relatively inexpensive and easy to do.
2. Check the blower motor fuse: Even though the blower works on high, ensure the fuse isn't blown. Check the owner's manual for the location and rating of this fuse.
3. Check the wiring: Visually inspect the wiring harness leading to the resistor pack and the blower motor for any damage, corrosion, or loose connections.
4. Check the blower motor switch: This is the least likely, but if the other checks come up clean, it might be the problem.
In short: While a relay *could* be the issue, the resistor pack is far more likely to be the cause of your blower motor only working on high. Start by checking and potentially replacing the resistor pack. If the problem persists, move on to the other troubleshooting steps. A repair manual specific to your 2003 Grand Caravan will be very helpful.
