My a/c was building up high head pressure and cutting off. I found the fan clutch was bad and changed it. I changed the low pressure switch at the same time. The a/c would run for about 5 minutes and the comp would cut off. I could switch it off on the dash for 5 minutes ,turn it back on, and it would work for 5 minutes. I connected the manifold gauges and pressures were basically normal. When removing the high side gauge I found the seal would not close completely all the time. Well, the freon leaked down and the comp would not come on until I charged the system again. Pressures at idle(then) were 40 Low, 200 High. When I raised the RPMs, Low would drop to 30 and the comp would cut off,then Low would go above 100 and stay, High would drop of course,until I let it sit for 10 minutes or more with a/c turned off at the controls. Turn it back on and same result. Any suggestions before the truck goes to a shop?