A/c Aircon Not Working. 2.8Crd Mk4

[718spider]

Hi all. I have a problem with the A/C on my 2005 Grand Voyager 2.8CRD and need some diagnostics help...

I bought the van two years ago and the A/C has never worked since I've owned it. First I tried the obvious option of having it re-gassed at Kwik-Fit. They pressure tested it and refilled it, but it still didn't work. The mechanic there suggested it might be the High Side Pressure switch, so I replaced that with a new ($40) one from the US. But that didn't work, still no A/C.
Last year, after a significant turbo failure and the effective 'grenading' of the engine, I had the whole thing expensively and extensively rebuilt (excellent job by Ring Engineering in Southall), but that (obviously) had no impact on the still malfunctioning A/C. They did take a look for me though and diagnosed that when the A/C was switched on power was getting to the A/C Clutch, but the clutch solenoid wasn't engaging. So, £80 later, with a new A/C pulley/clutch fitted and the system once again re-gassed.... still no A/C.

 

I'm reluctant to just start replacing more parts (like the whole compressor) as this is, obviously, a very expensive approach (and having already poured PLENTY of money into this rig I'm reluctant to spend more) and may not even fix the issue if it turns out it's electronic. But I really do miss not having A/C!!

 

So the help I'm seeking is for some kind of diagnostic process.  Can someone tell me how to attempt to diagnose what the specific problem may be? i.e. when and where should I be checking for electrical power? There are various relays and pressure switches in the system, so what should I be checking for and where? Is there a schematic available somewhere that could help?

 

Thanks in advance for any help that's forthcoming! ;-)