* Blend Door Actuator: This is the most common cause. The blend door actuator is a small motor that controls the flow of hot and cold air to the vents. If the passenger-side actuator is faulty, it might be stuck in the "cold" position, regardless of the temperature setting. This is a relatively easy fix, often involving replacing the actuator itself.
* Blend Door Cable (if equipped): Some vehicles use cables instead of actuators. If a cable is broken, frayed, or disconnected on the passenger side, it won't be able to properly regulate the air flow.
* Vacuum Leak: The HVAC system might rely on vacuum to operate some components, including the blend doors. A leak in the vacuum lines can prevent the passenger side from receiving the necessary vacuum to switch to hot air.
* Mode Door Actuator: This controls whether air comes out of the dash vents, defrost vents, or floor vents. If it's malfunctioning on the passenger side, it could be diverting the air somewhere else, even if the blend door is working.
* Restricted Airflow: Check the passenger-side vents for any obstructions. Something might be blocking the airflow, making it seem like the heat isn't working even if it is.
* Wiring Issues: A problem with the wiring harness connected to the passenger-side actuator or other components can prevent the system from functioning correctly. This is less common but possible.
* Heater Core (Less Likely): While less probable given the driver's side works, a partially clogged or leaking heater core could reduce or eliminate heat on the passenger side, especially if there's a blockage on one side of the core.
Troubleshooting Steps:
1. Check the Obvious: Ensure the passenger-side temperature control is set higher than the driver's side and that the fan speed is sufficient. Make sure vents aren't blocked.
2. Listen for Actuator Sounds: When you change the temperature setting, listen carefully near the HVAC system under the dashboard. You might hear a clicking or whirring sound from a working actuator. A lack of sound on the passenger side points towards a faulty actuator.
3. Visual Inspection: If you're comfortable working on your vehicle, you might be able to access the actuators and visually inspect them for damage. This will require removing parts of the dashboard.
4. Vacuum Check (Advanced): If you suspect a vacuum leak, you'll need to check the vacuum lines leading to the HVAC system using a vacuum gauge.
Recommendation:
Unless you have experience working on car HVAC systems, it's best to take your Jeep to a qualified mechanic. They have the tools and expertise to diagnose and fix the problem efficiently. Describing the issue as "passenger-side heat not working, driver's side working fine" will help them focus their diagnostic efforts.
