The heater control valve on the 190E is located BEHIND the firewall on the passenger side of the car. This has also been described by other posters as "behind the battery". The valve is located under the plastic grill that prevents leaves and debris from entering. There are four screws that attach the grill. To access them you must slip off the rubber seals that are on either side of the grill. They are not glued on and you should be able to manipulate them to remove them. Once removed, you will find four screws (two on the front and two on the rear of the grill). Remove the four screws and the grill can then be removed. You can now remove the valve. There are two short hose pieces (inlet and outlet) that you should replace when you replace the valve.