When I first start the truck the AC works fine but after driving around it will just blow warm air, sometimes it is for a few mins, other times it is till the truck is shut off for a few mins
It seems to do it more often when above 85 outside, and if I am at idle for a while ie stop light then get on the gas, not talking peeling tires just a little heavy.

Things I have done already. Replaced fan clutch with Motorcraft clutch. Washed the AC condenser and radiator.
I have checked the system pressures while running at idle and the pressure seem normal and I can see the fan clutch works as the high pressure side drops after a few mins running.

My next step will be pulling the charge and weighing in a new charge

 

Check the air gap when the engine is both cold and hot. I found when my Lariat's engine was cold, the air gap was within tolerance. After a few minutes of driving with the a/c on, the heat caused the air gap to expand beyond the clutch limits, and no a/c.

Fixed mine by removing one of the clutch shims so it's in tolerance hot and cold.

 

wab your blend door ?

 

I downloaded ForScan and drove around watching a couple PIDs mainly the high pressure and low pressure switch and the AC clutch allowed.

While at an idle all was good as soon as I stepped on the gas the low pressure would open if on the gas long enough the AC clutch allow would open.

So basically I was cycling the low pressure switch at anything above idle.

I pulled the gas and evacuated and weighed in the correct charge and it is ice cold now.

Checking the pressures again I think some air(non condenseable) was in the system as the hi pressure side was much lower with the same ambient temp

Drove around the again with ForScan and I could only get the low pressure to open after a long idle period but the clutch would not turn off