Heat and A/C stop when accelerating?

So this happens when the engine vacuum goes low under load. There is a vacuum storage tank (ball) under the hood I would make sure the vacuum lines do not have any holes/cracks. Also, the van may have a vacuum pump that is not working as well. I would turn the key on to see if the vacuum pump comes on. Also, near the vacuum storage tank there will be an inline vacuum check valve. If you remove it, you should be able to only blow through it one way, if both ways work the valve is no good. Check out the images (below). Let us know how it goes.