Luce, and whoever else is interested:
It sure looks like you have part winding start on those chillers. I could not see the contactor portion of the wiring diagram but from what you discribe, and the fact that you have some Star-Delta starters (which are different), leads me to think you are correct. I have never seen one on those machines but Trane did use P-W start on some of their recips.
Let me try to clear the waters a bit as I have met old timers in the business who did not really understand P-W, Star-Delta, Primary Reactor, Auto- Transformer, Solid State, VFD or the difference between open and closed transition. All of these terms apply to Trane, Carrier, York, W-House (McQuay) and any others. They also apply to sewage pumps,fans, the pumps trying to keep New Orleans dry, or any other large motor (read big electrical inrush load).
The motors you are talking about are 6 lead motors ( six terminals in the terminal box). Basically (as stated earlier) you have two seperate three phase moters in one housing. Remember the Ohm readings you got? The two motors are not interconnected inside the casing. but their ends are brought out to where we can get to them to perform our little tricks.
The simplest starter is an across-the-line. One contactor closes and "Bang" it's running at 100% torque and current draw. This may not be a good thing so we go to a P-W start. The simpelist of these requires two contactors. When C-1 closes the motor starts with only 65% current draw, but only has 48% of the torque. Hence the "unloaded " start. When C-2 pulls in we are at 100% torque and current draw.
A Star-Delta Starter requires a third contactor (and may have 4 along with big resistors in the starter).
Hope this helps a little and keep one hand in your pocket when working in these things, they wiil bite you.