1. Check the Obvious:
* Passenger Side Blend Door Actuator: This is the most common culprit. The actuator controls the blend door that mixes hot and cold air. If it's malfunctioning, it might be stuck in the cold position. You'll need to:
* Locate it: This is usually located behind the dashboard, often near the passenger side. Accessing it requires partial dashboard disassembly – this is a moderately difficult task requiring patience and potentially specialized tools.
* Inspect it: Look for broken gears, stripped gears, or any visible damage. You might be able to manually move the blend door with a screwdriver (after accessing it) to see if it's mechanically stuck.
* Test it: You *might* be able to test it with a multimeter (checking for power and resistance), but this requires some electrical knowledge.
* Replace it: If faulty, you'll need to replace the actuator. This is usually a relatively inexpensive part, but the labor involved in replacement can be significant.
* Passenger Side Temperature Control: Ensure the passenger side temperature knob isn't accidentally set to its coldest setting. Seems obvious, but it's worth a quick check.
* Vacuum Lines: The HVAC system relies on vacuum lines to control various actuators. A leak or disconnection in the line controlling the passenger-side blend door will result in it not functioning correctly. Inspect the vacuum lines for cracks, holes, or loose connections.
* Filters: A clogged cabin air filter can restrict airflow and indirectly affect the temperature balance, although it's less likely to cause only one side to be cold. Replace the cabin air filter as a preventative measure.
2. More Advanced Troubleshooting:
* Mode Door Actuator: While less likely to cause only the passenger side to be cold, a malfunctioning mode door actuator (which controls the direction of the airflow – floor, vents, defrost) *could* contribute to the problem if it's interfering with the blend door's operation. This requires the same level of disassembly as the blend door actuator.
* Electrical Issues: Problems with wiring, fuses, or the HVAC control module itself are less common but possible. Use a multimeter to check for power and continuity at the actuator connector and related components. This requires some electrical diagnostic skills.
* Blown Fuse: Check the owner's manual for the fuse related to the HVAC system.
* Refrigerant Level (Less Likely): While a low refrigerant level would generally cause both sides to be cold, a severely restricted system *might* lead to uneven distribution of cold air. This is less likely to be the sole cause of this specific issue.
3. Steps to Take:
1. Check the easy stuff first: Temperature knob setting, vacuum lines, and cabin air filter.
2. Consult a Repair Manual: A service manual for your specific 2003 Jeep Grand Cherokee will be invaluable. It will show you diagrams of the HVAC system, the location of components, and the steps for disassembly.
3. Consider Professional Help: Accessing and repairing the blend door actuator requires significant mechanical aptitude and knowledge. If you're not comfortable with this level of car repair, it's best to take it to a qualified mechanic specializing in Jeep vehicles. The labor costs to diagnose and repair this issue can be high, so it's important to weigh that against DIY efforts.
Remember safety first when working on your vehicle. Disconnect the negative battery terminal before starting any electrical work. If you are unsure about any step, consult a professional.
