I have the fix for this been down the road from hell on this one.You have a 8780xp because it is not a problem on the 8780.There is a kit 71410513 to fix this but it did not work.But I came up with a different way to run the belt so you get more wrap around the fan hub.When the ac kicks on the belt slips on the fan hub, the belt gets hot and you are done.You need to have the kit installed to make this work.You need a different belt cummins n3290018 it is 6 inches shorter than the one that comes with the kit.It goes over the fan pulley UNDER the ideler and around the alternater to the tensioner over the water pump around the crank shaft and to the fan.This is the fix and agco rep is coming to see what I did so they can get the word out.You need to make sure your fan hub is not worn out,you might need to replace it.I have helped two other people with this problem.I have 250 hours on this belt and it is still going.Its just a matter of time and conditions before all 8780xp owners go through this.It is a problem on 9690's and R 65 Gleaners.Massey did not have an answer or Cummins.You can call me at 1 509 520 5474 if you have any questions. good luck
