ac runs then blower starts blowing lightly then no ac shut off 20-30 minutes turn back on and is cold 20 minutes then blower deminishes then shut of30 minutes. Clutch turning had orphice tube changed full charge still does same thing This is after changing evaporator in 2008 ($1000 at dealer) only does when your on long trip

 

how many miles on truck? your serpentine belt might be slipping when getting warm. should be changed every 80000 miles.