2001 town & country front and rear both blowing cold air. When you first start out they will blow hot then turn cold. Front fan stops working then will start again after you turn off vehicle or it decides to blow warm air again. Back fan works all the time but blows cold air. Temp on gages a bit warmer than normal but not very much. Changed thermostat and radiator cap. Flushed radiator and checked levels many times. No air in radiator. Had system pressure tested and its fine. I can hear mixer door open and close. We are at a loss any ideas?