Here are a few things you can check:
1. Low coolant level: If your vehicle's coolant level is low, the heater core, which is responsible for heating the air that comes through your car's vents, may not be getting the heat it needs to function properly. Check the coolant level in the reservoir typically located under the hood and ensure it's between the "Full" and "Empty" marks. If it's low, add the appropriate coolant to reach the correct level.
2. Faulty blend door actuator: The blend door actuator is a device responsible for regulating the air that flows into your vehicle's cabin. If the blend door actuator is faulty or malfunctioning, it may improperly mix the warm air from the heater core with the cold outside air, resulting in cold air on the passenger side.
3. Clogged heater core: Dirt, debris, or mineral buildup can clog your vehicle's heater core, restricting the flow of hot water and preventing it from properly heating the air. If the heater core is clogged, flushing it or having it professionally cleaned may solve the issue.
4. Problems with the heater control panel: The heater control panel is what you use to adjust the temperature and fan settings inside your vehicle. If the control panel is malfunctioning, it may be sending incorrect signals to the blend door actuator or the fan, leading to a disparity in the temperature of air on the passenger and driver sides.
If you've tried checking the coolant levels, inspecting the blend door actuator, and cleaning the heater core, and the issue persists, it's best to have a certified mechanic diagnose and repair the problem for you.
