08 Ford e250 intermittent AC

Works great at idle but when you put engine under strain like leaving a stop light, AC cuts out until you get up to speed, when engine is not under strain, AC kicks back in. Any ideas??

Some vehicles have a switch the disengages the AC clutch when the manifold vacuum drops, I.e. when under load…

That switch and its input data (vacuum? throttle position? other or a combo?) are the first place to look.