Generally, there are two possibilities:
* Blend Door Actuator: This is the more common culprit for heating/cooling problems. It's an electric motor that controls the blend of hot and cold air. It's usually located inside the dashboard, and requires partial disassembly to access. This is *not* a valve in the traditional sense, but controls the airflow. Problems with this often manifest as inconsistent heating or cooling, or the inability to switch between hot and cold.
* Water Valve (Less Common): Some Ford Explorers might have a separate water valve that controls the flow of coolant to the heater core. This is less likely to be the source of the problem compared to the blend door actuator. Its location would vary, possibly near the firewall.
To determine which is causing your issue:
1. Diagnose the problem: Are you getting no heat at all? Does the heat switch between hot and cold erratically? Is the problem intermittent? This will help narrow down the culprit.
2. Consult a repair manual: A repair manual specific to your 2004 Ford Explorer (with the correct engine size) will show you diagrams and locations of these components. Online resources like Haynes or Chilton manuals can be helpful.
3. Use a diagnostic tool: A code reader can sometimes detect issues related to the HVAC system. This might point you toward the blend door actuator.
Without knowing the exact symptoms, it's impossible to pinpoint the exact location of the relevant component. If you're experiencing heater issues, it's *more likely* to be a problem with the blend door actuator than a separate water valve.
