Brother-in-law mechanic just replaced the heater core and thermostat in our 2000 Durango. This has resolved the foggy windows but now we have barely any heat at all and always icy cold air blowing in on our feet! No matter what setting we have the system set at (defrost, floor, dash) there is ALWAYS air blowing from the dash vents. Have already "burped" the cooling system. Covered radiator with cardboard to try to increase the temp of the coolant. Runs about 180-190 degrees with or without the cardboard. Any suggestions?