I jumped the compressor clutch whilst the car was running and I get nice cold air through the system, so fundamentally the system is ok and the fault is electrical.
As per Iain's message (Thanks you for the tip Iain), I'd hoped that this would 'kick' the switch as it is on the High side, but no joy. I removed and re seated the switch but no joy.
The pressure switch has a closed circuit between the middle two pins. according to
that is pin 1 & 2 request for Aircon and Enable, suggesting that it is in the right pressure range and the aircon should work. but the diagram on the link disagrees his post and with the pins I buzzed out. eLearn differs again saying request and enable are pins 5 and 2 (which counting the pins left to right would be the pins I would say are closed circuit)... but nothing on the connector is labelled.
If I remove the switch so pressure is ambient (low) the connection from the middle two pins goes open circuit so I think the switch is ok... :-/
I tried to buzz out the feed from the Relay to the connector to the Comp but it isn't connected directly. following the loom the line to the compressor goes via the ECU on the back of the pellum green wire with red stripe.. but there are two green with red stripe in the loom at the other end..... ugh...
So I go to check the manual to ensure I have the right relay & fuse.... and the manual is completely different! I presume it is for the other GT's not the v6.
the label under the cover shows the relay as T05 in slot 2, if the label is upside down that would be slot 5... I'm now completely baffled.
So i'm stuck and frustrated.
Any other tips?