The blend door actuator on a 2000 Cadillac Catera is located
within the dashboard, behind the glove box. Accessing it requires significant disassembly of the dashboard. It's not a simple job and typically involves removing the glove box, parts of the center console, and potentially other interior trim pieces to reach the HVAC system housing where the actuator is mounted.
Because of the complexity, this is usually a job best left to a qualified mechanic. A repair manual specific to your year and model Cadillac Catera will provide detailed instructions and diagrams, but be prepared for a significant undertaking.
