There's no single answer. To find the correct information, you'll need to:
* Check your vehicle's documentation: Your owner's manual should list the specifications, including the AC compressor model.
* Look at the compressor itself: The compressor will have identifying numbers stamped on it. You can then use these numbers to search online for the specific model.
* Use a vehicle identification number (VIN) lookup: Many online parts stores allow you to search by VIN, which will provide you with a parts list specific to your vehicle.
Without more information about your specific 2001 Dodge Ram, it's impossible to say what compressor it uses.