Intermittent cooling in a 2006 Hummer, H3, five cylinders?

Sometimes the a/c cools perfect and other times not at all and sometimes in between, it is better when the vehicle is cruising (50-60 MPH) but this weekend in a long trip just stop working, low side pressure is low and high side is high, I suspect the expansion valve and the radiator fan clutch, how do I test those components?, there is no overheating or other conditionIntermittent cooling in a 2006 Hummer, H3, five cylinders?My Hummer advisor says that engine rpm's are critical to the function of the ac system. Usually a dirty throttle body can affect the engine rpm's. I would try a throttle body flush and new filters, before I would resort to any drastic measures.