I've just bought a Hymer Tramp on A Fiat Ducato 2004 base. We I got it home I found both the passenger and driver's cab electric windows were not working. I also found:
1. The electric door locks work OK
2. The windows were glued to the rubber seals with mould. The van has not been used in a long while (2004 with 17000 miles on the clock)
3. The fuses (R/H side fuse box) are all OK
4. I hear a click in the fuse box when I press the window switch. Does this mean the relay(s) are OK?
5. I've stripped the passenger side door to expose the workings. There is a 2 wire connector going to the regulator. I presume a +ve feed from both one to drive the window up and one to drive the window down? As a test on the regulator would it be safe to put a 12v supply directly on one of these cables to test the regulator? Thus if it worked it must be the relay?
6. Can I safely swap relay in the box to test them? (they all look the same)
Any advice would be much appreciated - thanks

Had the same trouble myself, firstly they have a habit of jamming, so while someone is pressing the switch with both hands one on inside one on outside, try pulling downwards,
if you have suction pads better. If not try this next.
As you say the fuses OK, pull the two cable connectors to the motor apart in door, put a meter across see if power is there when switch is pressed, if so suspect it to be
the regulator/motor gone,
As it stood for a while think the motor is stuck & pulling down may release them.
Otherwise its new regulators.
Got mine from EuroParts, cheaper.
You will need to take off the nuts, cut the two cables so the window drops to get access to the pin in centre bottom of window, pull out plastic cerclip on one side pull
out pin, then regulator/motor can be taken out and new one replaced.
Hope there only stuck.

Fixed the problem. The plastic drive spirals in the motors (yes - same problem both sides) had somehow disengaged. I unbolted to each motor to reveal the drive spiral then re inserted it. The cogs/spirals now engaged - problem fixed. A 2 hours job - saved myself a fortune over new regulators. The motors are reasonably accessible - no need to remove the glass or the frame.

Make sure to spray the rubbers with silicone spray takes a lot of stress off the motors and gears, they often strip the plastic cog so you were lucky.

Have just solved problem at no cost except time
Remove all door trim
Undo 3 nuts holding motor
Undo nuts holding centre window guide and push out ( may take some force at top)
Window motor can then be accessed without undoing guide wires, to remove 2 screws at top. It may not come apart completely, but you should be able split motor and gearbox sufficient to blow out gently with an air line and squirt in liberal amounts of WD40, reassemble motor and test for movement before reversing above