Hi, this is for a corsa c compressor but I would assume they are all the same, the system is fully charged with 12v getting to the compressor when the button is pressed the clutch wont engage, I have bought a 2nd hand one off a breakers, when I connected the 12v from the pressurized system to the clutch on the new unit the revs rise as they did with the 1st unit but once again I can not hear anything clicking in the compressor & the pulley spins by hand and not the center is there any way to check the unit works before I fit it & refill the system and waste more money.