I beleive you are talking about the heaterdore inside the car that suplies heat to the interior?If so,there are cooling systems flush kits that you can get atuo parts stores and can work,do it twice to be sure.You can use a garden hose to try and clear out the core and switch it from side to side to reverse flush the core.If this does not work,you need to replace the heater core,mrmopartech
