QUOTE=carringb;277991]That looks like factory air. The rear air only has an orifice tube, rather than an expansion valve. It is connected to the rear evaporator. It can plug up from debris. In my case, sloppy body shop didn't cap the lines while they were open, and it plugged with bondo and primer dust. It can also plug with debris if the compressor went out. It's only a $10 part or so, but does require doing a full evac and recharge. This is pretty much the only place where you could have a restriction. The rear factory a/c simply tees off the front.[/QUOTE]
That is indeed factory A/C---are there any rear headliner function controls on this van? They would be in the headliner between the front seats and the second row bench or bucket seats.
My 2005 E350 EB had a TXV, the FOT only on the front evaporator only. I believe on the factory A/C systems those are pretty much required to adequately cool the rear area. That could have failed and blocking refrigerant flow. Sadly its installed on the evaporator inside the rear heater & A/C housing. According to my Ford parts guy the TXV is part of the evaporator and not sold separately through them.
Dealer cost to me on the complete evaporator w/TXV would be $263.89, part number 6C2Z-19860-B.
They do seem to be available in aftermarket sources though.
Here's a Ford drawing showing a 2006 E-Series with factory air:
That drawing is captioned at the top as used on a 2006 E-Series with factory rear A/C.
The exact drawing for the OP's particular van can be found using the VIN and perhaps contacting a local Ford dealer.
Dealer cost to me on the complete evaporator w/TXV would be $263.89, part number 6C2Z-19860-B.
The TXV by itself do seem to be available in aftermarket sources though. Four Seasons brand through almost any parts retailer.
HTH