1. Blend Door Actuator(s):
* What they do: These small motors control the blend doors that mix hot and cold air before it reaches the vents. If one actuator fails or is malfunctioning, it won't correctly mix the air, leading to one side being hot while the other is cold. You likely have separate actuators for the driver and passenger sides.
* Troubleshooting:
* Listen carefully: When you turn the AC on, listen near the HVAC unit (usually under the dashboard). You might hear unusual grinding, clicking, or whirring noises – signs of a failing actuator.
* Visual Inspection (Difficult): Accessing the blend door actuators often requires partial dashboard disassembly. This is not a simple task and may require professional help. If you can see them, check for obvious damage or loose connections.
* Diagnostic Scan: A professional mechanic can plug a diagnostic scanner into your car's OBD-II port. While it might not directly diagnose a blend door actuator issue, it could reveal related codes pointing toward the HVAC system.
2. Blend Door Linkage:
* What it does: This is the mechanical linkage connecting the actuators to the blend doors. It can become worn, broken, or disconnected, preventing proper operation.
* Troubleshooting: Again, this usually requires access to the HVAC unit, making visual inspection difficult and often necessitating professional help.
3. Low Refrigerant:
* While less likely to cause a *one-sided* problem, low refrigerant can lead to inconsistent cooling throughout the entire system. Check for leaks or have a mechanic perform a refrigerant charge check.
4. Vacuum Leaks (Less Common):
* Some older vehicles use vacuum lines to control blend doors. A leak in these lines can lead to improper operation. This is less common in later model vehicles but still possible.
5. Electrical Issues (Rare but possible):
* A faulty wire or connector to the actuator could prevent it from receiving power.
Fixing the Problem:
* DIY Repair (Advanced): Replacing a blend door actuator is possible but requires significant mechanical skill and familiarity with automotive systems. It typically involves accessing the HVAC unit behind the dashboard, which can be time-consuming and complex. Consult a repair manual specific to your 1998 vehicle model.
* Professional Mechanic: The most reliable and often most efficient solution is to take your vehicle to a qualified mechanic specializing in automotive air conditioning. They have the tools, expertise, and experience to diagnose the problem accurately and perform the necessary repairs.
Before you start any work:
* Disconnect the negative battery terminal to prevent electrical shorts.
* Consult a repair manual specific to your 1998 vehicle for detailed instructions and diagrams.
The complexity of accessing the HVAC components makes this a challenging DIY repair. Unless you're very experienced with automotive repair, taking it to a professional is the recommended approach to avoid further damage.
