My 2001 E350 Club Wagon XLT AC only blows about 50 degrees from the dash & 60 degrees from the rear.
I replaced the compressor, condenser, accumilator, orfice tube,flushed the system & checked the heater control valve at rear evaporator. I've watched the engine fan and the clutch does not appear to be slipping.
On cooler days and at night time system seems to work much better. But during hot Texas days it doesn't work very good.
You can contact me at jsouth111@yahoo.com