A/C issues?

[ArkansasRiceman]

Howdy all

So here is the issue and it is one that I myself have never seen. When I start my truck and take off down the road the air conditioning is blowing warm air even at speed. Now the funny thing is I can stop the truck, kill it and then start it back and it starts blowing cold. I have replaced the tube in the a/c line, changed out the pressure switch that is located by the frame on the passanger side, checked the high and low pressures on the a/c system, engine coolant is fine and the radiator is clean. I just have not ever heard of anything like this and I was wondering if anybody here has heard of this type of thing? Its going to start getting hot here in Arkansas pretty soon and we start watering rice here soon.