2005 Ford transit connect drivers side window problems

[Danny1997]

Just bought a 2005 Transit connect lwb. Having problems with the drivers side electric window, sometimes it works but then itll drop and not come up .

The passenger side one is fine and ive tested the motor on the drivers side by plugging the passenger side cable into the the drivers side motore and it works fine. 

Any ideas on what could be the cause for this?

Thanks in advance