L322 aircon tensioner pulley

Morning all
The aircon tensioner pulley and belt were missing from my 2002 L322 TD6 so it's no wonder the aircon doesn't work.
Anyway, I got a belt and a pulley but I can't get the belt on.
Is the arm that the pulley is mounted on supposed to rotate so that it automatically tensions the belt.
Mine won't move
Thanks

I still can't get the aircon belt on, so either the tensioner isn't moving enough or I've got the wrong belt
The belt I have is a Gates MICRO-V 5PK810 https://www.gates.com/gb/en/search.p.8552-000000-000001.v.8653-10073.html
Anyone know if this is the correct one and / or is the tensioner prone to restricting movement?
Thanks

Looking at Rave this looks the same as my D2 one that was seized in the housing

That's the one
It does rotate a bit, but i don't know how much it should move, I just know that the belt is putting up a hell of a fight against being put on.
Is the tensioner openable / repairable?

Mine was seized solid and wouldn't free off. If I remember correctly my used replacement was a bit stiff as well so I stuck it in the vice and used a lever and plenty of oil to free it off.

Thanks, I'll try persuasion and lubrication (but not necessarily in that order)

At least yours already moves a bit so you're half way there.

All the way there now thanks
Bit of muscle and North Sea finest (not necessarily in that order)

My IID tool is saying that the temperature demand for the drivers side of the passenger compartment is 5 deg C so that explains why the aircon is constantly demanded 'on'.
According to the manual, 5 deg C is way outside the possible demand of between 16 and 28 deg C,
Turning the control knob doesn't alter the 5 deg C demand
I'm guessing that there's something wrong inside the control panel.
Any thoughts anyone and does anyone have any experience of working on one of these?
Thanks

Another wee question for you knowledgeable people.
I've replaced the aircon compressor and haven't yet got the system gassed or oiled so I've disconnected the clutch plug to make sure that the compressor doesn't turn until that happens. Probably i didn't have to do that because the pressure sensor should stop that anyway and I've checked the the system isn't trying to engage the clutch when I turn the passenger compartment controls to 16 deg C
The IID tool is showing the sysem has 5 bar of pressure which I thought was far too high for an empty system, so I disconnected the sensor plug and the pressure showed 30 bar, which i think means the sensor is probably ok
The manual says that the system will run with the pressure between 2.8 and 33 bar, so why isn't there a demand for the clutch?