@ronnie5

I would bet it is how the sequencing of the chillers is set up in the automation system. sorry in advance for the essay, but below is how this typically works.

Its very common for them to cycle chillers between lead and lag over some programmable period of time to spread out the operational hours. This is how it will typically work

When BAS Calls for Cooling
> The Lead Chiller is Enabled and runs off internal controller logic to maintain the leaving water temp
> if the lead chiller is at 100%, and there is more load, the loop temp will continue to rise.
> if its still rising, and there is no alarms, the BAS, or the chillers internal logic will notice that we need more load, and it will start the Lag chiller
> once it starts the lag chiller, the lag chiller will also run off of its internal logic to maintain leaving water temp.

The way they do the transition to the lag chiller varies, sometimes they will override the chillers controller, and unload the Lead chiller by 15-20%, start the second machine, and bring the Lead chiller back up to 100% before loading the Lag. Sometimes both chillers can be set up to talk to each other, and do most of this through the internal logic, so the Lead chiller starts the lag chiller, and not the BAS system.

There are tons of ways to do it, but its very common to see a lead / lag setup in a similar way to this on most commercial applications.

This is a 134A chiller Discharge superheat is 19 I think it should be closer to 15 on the YK. also the delta on the condenser water is a little high not by much. PRV position only 16 % @100% FLA. This explains higher then normal Oil temp in sump due to vanes being closed down some and the heat of compression adding to oil traveling thru compressor. I would check flow rate and see if it could stand a lil more charge. maybe other issues just a quick glance