Ford does not use a cutoff valve on the heater core in this vehicle. This means that coolant flows through the heater core whether you're using it or not. When you're not using the heat, a door closes preventing air from flowing through the heater core. Instead the air flows around it. The evaporator, the part that makes the air cold with the AC on, is on the passenger side of the vehicle. The blend door is probably only partially open, but by the time the partially warmed cold air gets to the driver's side- it's warm.
I hope that helps, I think you're going to need to take it to the dealer to find someone who can figure it out.
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Originally Posted by the user formerly known as ZX3_Chick
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