Recently bought a D9 and believe the air con doesn't work.

If you turn it on manually, or let the climate control do it, the A/C symbol on the MFD lights up, but no cooling.
I've proved the compressor clutch doesn't operate. (It does if connected directly to the battery, but I've only tried this with engine stopped).
Checked, (I think), the pressure switch after seeing Puggy's leaky one - mine shows no sign of leakage, but it's only got 3 pins unlike the 4-pin example in Puggy's pic. Not sure if this is indeed the pressure switch, it's mounted vertically, (connections upwards), on a block on the driver's side of the condenser.
I've examined the condenser, compressor, pipework & hoses and found no sign of leakage.
Having studied most of the relevant posts on this site, I'm thinking two possible causes:
1. No gas / faulty low pressure switch so system wont let it run.
2. Faulty BSI relay, therefore no power to compressor clutch.
Now I don't mind paying for a recharge, or pulling the BSI out & swapping the relay, but I'd rather not do the former more than once or attempt the latter without proving conclusively it should be disturbed.
So I'm hoping someone can has a circuit diagram for the aircon, can tell me how to (briefly) bypass the LP switch, or knows which relay / output terminal should be powered when the BSI enables the compressor. (Haynes useless for this).
Any other suggestions gratefully received.
Apologies for lengthy post, thanks for reading it all!
Eric