Here's why:
* Blend Door Actuators: These small motors control the blend of hot and cold air that goes to each vent. If the driver's side actuator is malfunctioning (stuck, broken, or simply failing), it might be unable to correctly position the blend door to deliver the temperature you've selected. It's stuck on "hot."
* Other Possibilities (less likely):
* Blend door itself: While less common, the blend door itself could be broken or jammed. This is usually diagnosed *after* checking the actuator.
* Vacuum leaks: Some older climate control systems rely on vacuum to operate. Leaks could disrupt the proper functioning of the blend doors.
* Wiring/electrical issues: A faulty wire or connector to the actuator could prevent it from receiving the correct signal. This is less probable than a bad actuator.
* Core or Heater issues (if only hot): It's unusual to have one side cool and the other hot *unless* there's a problem specifically with the blend door. A faulty heater core would make both sides hot.
How to Diagnose:
1. Check the actuator: This usually requires some disassembly (removing parts of the dashboard). You'll need to locate the actuator (usually near the HVAC blower motor) and see if it's moving freely when you change the temperature settings. A visual inspection might reveal a broken or jammed mechanism.
2. Listen carefully: With the climate control on, listen near the dashboard vents. You might hear unusual clicking or grinding sounds from the driver's side, indicating a struggling actuator.
3. Advanced Diagnosis: Using a multimeter to check the voltage and resistance at the actuator can help determine if it's receiving power and if the motor itself is functioning.
What to do:
* Replacement is usually the solution: If you find a faulty actuator, replacement is generally the easiest and most cost-effective repair. You can find these actuators online or at auto parts stores. However, replacement can be tricky involving dashboard disassembly, requiring some mechanical aptitude or professional help.
* Professional help: If you're not comfortable working on your car's dashboard, take it to a qualified mechanic or HVAC specialist. They have the experience and tools to diagnose and fix the problem efficiently.
Remember safety first when working on your vehicle's interior. Always disconnect the battery before working with electrical components.
