It sounds like a control problem. There is only one compressor and
condenser, and since you have cool air at the front, it is likely the rear
evaporator is also being cooled (I assume you have a system with the true
rear A/C, not just vents in the back of the console). It seems likely that
the blend door in the rear compartment is either stuck, or you have a
problem with one of the controls. Unlike the main heater, the mode and blend
doors in the auxiliary (rear) A/C unit are electrically operated. So it is
possible you only have a blow fuse (check fuses 7, 23, and 24 in the main
under dash fuse panel).
Does it make any difference whether you try the front or rear controls for
the auxiliary unit? If not, I would remove the rear interior quarter panel
trim so I could get at the auxiliary A/C unit to see if the blend door motor
is getting power.
You should join the Expedition Owners mailing list and ask your question to
that group (see http://xpog.com/mailman/listinfo/expedition_xpog.com ).You
might all so ask the experts at www.flatratetech.com .
OR.. if like earlier versions, the back unit has a TXV (expansion valve)
control. (and these play he!! with trying to fill the system by touch..
dont do it)
This TXV could be bad or plugged... you need remove enough trim to see
and touch the lines.
If the coils getting cold but not freezing, then it's fine and problem is
blend door controls, etc.
If the coil's freezing then the txv is bad or the probe for it is not on
the lo side line.
If the heater core is hot, check to see if the heat control valve in
heater line is bad or disconnected.
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