Also, are you referring to the minimum cooling load (tons), or minimum compressor motor load (amps)? They are not the same thing.... I am not familar with that machine, but I have seen others unload to 10%, or less, of capacity, but still run loaded at about 30-40% motor load.
Depend of the software and the administrator privileges you have over the program.You can make this machine to unload and load depend of the vain,slide,compressor speed etc. and whithout the knolege of the software and the machine mechanical minimum requirements is risky business.
There is no 10% or 40% ,depend on yuor loop load and the process the chiller is used for.I assume for 500 T chiller there is a option to increase artificialy the loop load and then to run in minimum load.What proces they use and how many cirquits on the loop they have,how many pumps,tower controls etc. is a complex issue.