Power side door not working

On my 97 Transport, it was 1 of 3 things that I fixed all to make it work.

1 was the contact block, with the problem in the door, pins inside the door corrosion ate away where the wires contact the sliding pins. I fixed it, but typically it may have to be replaced if bad.
2 which sounds mainly your problem, is the actuator that opens the latch, snapped the plastic arm causing it to work as your saying, only when you manually open the door. I got a factory replacement from Ebay and cured that problem.
3 On mine the contact safety switch which is part of the rear latch of the door, had literally lost the contacts, requiring replacement. This switch tells the sliding door computer, that the door is in fact fully closed or open.

You can tell if the actuator is bad when you press either the console switch, pillar switch or the remote FOB switch, you hear a noise similar to unlocking the door, but then it fails and does not cause the outside handle to move at all. You can more easily tell once you get the door trim removed, and are able to visually inspect it. Removing the door trim is however not an easy task, so you likely will want a mechanic to fix it. If you order the actuator from Ebay, you will find it comes with a set of replacement plastic clips/pins as they will break off sometimes when you remove the panel.