Hello Jeff D and Christian,
I'm using AECOsim SS6 08.11.09.866
I am also able to connect the components in the file Jeff posted. The connection points on the equipment and fittings are 'on the equipment'. For example in the exaggerated components (the VAV for example) the mechanical connect points are on the 'faces' of the ends. Here's an screen capture to hope explain it better:
In that image I had changed the line weight of the components to 8 to exaggerate them. On the VAV box round end there is a point on the center of the face of the round 'hole', on the rectangular end the four corners can be snapped to. On the valve they are basically center points on the face of the ends. I notice on the valves a connection point 'point' (in cyan in the capture) is out on the end of the Connection 1| Length (L1) property which is not where the connection point actually is. The plumbing example shows the pipe connected to the valve, so the center line of the pipes are snug to the face of the valve.
The exaggerated connection ends (as Jeff wrote in the .dgn file) I think of as 'sleeves' (maybe not the engineering term for those). The VAV, transition piece and the valve have the same datagroup property: Connection | Length 1 (L1) and Connection | Length 2 (L2) that control the length of the 'sleeve'. The connection point does not extend to those.
I tend to use the wireframe display style when editing mechanical components, where I can easier see the connect points. Although I find it's pretty easy to work in one of the rendered modes and get to those points. They're there and you'll see them when you highlight and select components. I'll switch between wireframe and illustration | without lighting. Hidden line works well for sometimes in the mechanical models. And I like using monochrome with shadows when I'm looking at the whole system, can see where things are going over-and-under, etc.
I also rotated the view to better find the round end point on the VAV, I kept snapping to the endpoints of the control box and VAV itself the way the view was initially rotated, because the point was 'behind' all those points.
One thing you will find is that rectangular components can connect with a center point or the corners. I was able to move and connect the transition to the VAV with any of these points on the transition to the corresponding points on the VAV shown above.
On the pipes and the round duct VAV end, I find I can use the center snap mode and that is the connect point. On the valve I could center snap to any of the circles on the face of the end and they would all connect. And you can get to the connect point on the round VAV 'hole' with the center snap mode. I use AccuDraw for center, nearest and intersect all the time. F11 to move the focus to AccuDraw and C, N and I shortcuts respectively.
The 'shroud' of points are there and are dimension keypoints. They are basically there and will get snapped to.
Jeff, I appreciate the time to create the example and write it up in there and post it. And Christian for posting the video.
Thanks