Run Defraggler via Windows Scheduled Tasks

I am trying to automate most of my computer maintenance. I have successfully ran CCleaner via windows scheduler but have failed to do the same with defraggler.

I am running df.exe with the parameter C:\ /large

When i run the scheduled task, cmd prompt comes up, runs a few lines (fast, cant read it) and cmd prompt then closes.

Is defrag running? i could not find an instance of it running in my applications or processes tab.

I am almost positive i am to run df.exe instead of the normal program to allow cmd commands.

Any help? thanks!