* Faulty Defroster Motor/Blower: The motor or blower responsible for directing air to the windshield on the driver's side might be malfunctioning. This is the most likely cause.
* Blocked Air Ducts: The ducts leading to the driver's side windshield defrost may be blocked by debris, ice, or even a malfunctioning vent actuator.
* Electrical Problem: A broken wire, faulty switch, or blown fuse related to the driver's side defrost could prevent it from working.
* Vacuum Leak (Less Likely): Older Cadillacs sometimes used vacuum systems to control some aspects of the climate control. A leak could disrupt the driver's side defrost function.
* Previous Repair/Modification: Someone may have incorrectly repaired or modified the system in the past, leading to this asymmetrical function.
In short, the car isn't *designed* this way. You need to investigate the underlying mechanical or electrical issue to fix the driver's side defrost. A qualified mechanic or someone experienced with classic car HVAC systems would be best equipped to diagnose and repair the problem.
