I am looking at a Trane CGAC chiller that uses a W7900 controller. The chiller is set up to use only one of the two circuits (100 of the 200 nominal tons), which is sufficient for the application. So it has traditionally run only Compressor 1. Compressor 1 recently failed, which shouldn't be a problem - we just switched compressor #1 "off" and compressor #2 "on". However, there is no lead/lag switch on this chiller. Previously, the W7900 was set to three stages (using the bottom dial), which made it work correctly; it loaded and unloaded compressor 1 in accordance with the setpoint and delta T dials (top and middle).
But it's not that easy anymore. Changing the dial to six stages (the default) makes the controller go through the first three stages on the non-operating circuit one before engaging the operating compressor at all, and then compressor 2 starts unloading WAY too early.
Is there a straightforward way to swap the compressor sequence so that stages 1-3 would operate the compressor that is in position 2? I considered getting out the wiring diagram and starting to go point-by-point through the control wiring, and will do that if needed. But I hope that there is a "swap these connections" type of fix. I can't be the first person that has dealt with this before, right?