Report "1996 Dodge Caravan 2.4 liter 312.000 km.Not enough heat coming from blower motor when set on maximum speed .The blower motor works well but only produces minimum heat .Replaced water pump , thermostat ,flush engine coolant.After this was done there was no significant improvement in the heating .What is the likely cause for this problem to occur. In the engine compartment I have notice two lines going to the heater core one supply line the other return line.One line seem to some kind of device in the tube with an arrow pointing .Is this device some how restricting the coolant flow to the heater core ? thereby diminishing the heat"