* Blend Door Actuator: This is the most common culprit. The blend door is a flap inside the heater box that regulates the airflow between the heater core (hot) and outside air (cool). A malfunctioning actuator (the motor that moves the blend door) could be stuck in a position that only allows hot air to the passenger side. This requires accessing the heater box, often a somewhat involved process.
* Blend Door Linkage: Even if the actuator works, the linkage connecting it to the blend door could be broken or disconnected, preventing the door from moving properly. This also requires access to the heater box.
* Vacuum Leaks: Some older vehicles use vacuum lines to control the blend door. A leak in these lines can prevent the door from moving correctly. You'd need to inspect the vacuum lines for cracks or disconnections. A hissing sound near the heater box might indicate a vacuum leak.
* Heater Core Issues (Less Likely): While less probable given you're getting heat on one side, a partially clogged heater core or a leak *could* restrict flow to the driver's side. However, this usually results in reduced heat overall, not a complete lack of heat on one side.
* Cable Issues (Rare in this model): While less common in 1992 models, some cars of that era used cables instead of a vacuum system. A broken or disconnected cable would prevent proper blend door operation.
Troubleshooting Steps:
1. Check Vacuum Lines (If Applicable): Inspect the vacuum lines leading to the heater box. Look for cracks, loose connections, or evidence of leaks.
2. Listen for Actuator Motor Sounds: Turn the heater on and off. Do you hear any clicking or whirring sounds near the heater box? A lack of sound suggests the actuator motor might be faulty.
3. Manual Blend Door Test (Advanced): This requires accessing the heater box (usually by removing parts of the dashboard). Once inside, you can manually move the blend door to see if it's free and responds. *Only attempt this if you're comfortable with automotive repair and have the necessary tools.*
4. Professional Diagnosis: If you're not comfortable working on your car's HVAC system, it's best to take it to a qualified mechanic. They have the tools and experience to diagnose the problem accurately and perform the necessary repairs.
Remember safety first! Disconnect the battery's negative terminal before working on any electrical components. If you're unsure about any step, consult a repair manual specific to your 1992 Buick LeSabre.
