The heater control valve on a 2000 Ford Windstar is located
inside the passenger compartment, under the dashboard. It's not easily accessible and requires partial disassembly of the dash to reach it. It's typically part of a larger blend door assembly that controls the temperature of the air coming from the vents. You won't find a separate, easily identifiable valve like you might on some other vehicles.
Because of its location and integration with other components, replacing it is usually a job best left to a mechanic. It's a complex process involving removing the dashboard trim and possibly even the glove box.
