My 1999 Ford Expedition air works in the back well, barley cool on drivers side and warmer on the pass. side?

Question

5.4 liter, auto temp control,front and rear controls,

Answer 1

Ford has a problem with the blend air doors inside the ducting system. Make sure the doors are closing all the way. It sounds like you are mixing heated air with your cold air. These doors are electronically controlled but the adjustment can change and cause them to not close all the way. It does not take very much leakage to warm up cold air.