i have a 2008 town &country limited with a 3 zone ac unit. It is a 4.0 6 speed if that matters.it only makes heat when you set the temp on high, not the blower speed , the temp control. You can set temp on low,61degrees,88 degrees and you get all cold air--- set temp on HI and you get all heat. This is true for all 3 zones. You can however set one zone on Hi and get hot air and set another zone on any temp and get all cold air.The problem seems to be a single problem common to all three zones. Can it be the temp sensor that reads cabin temp??If so is it in the overhead consol and how do I replace it??? If not then what??? Any help greatly appreciated ---I need a copilot to operate the heater since it is all hot or all cold.