OK after Ford gave up, I took it to a A/C specialist who also checked the obvious things and said it is definitely an auto-electrical issue.
Its spent the past 2 days so far at an auto-electrician who has come to the conclusion that its an
ECU fault.
He's said their 2 options are to either
1) locate a second hand
ecu and reprogram it, or
2) wire up the A/C old school style with another pressure switch and thermostat and wiring to bypass the
ECU.
Anyone ever heard of this type of thing before? Wouldn't a fault with the
ECU normally show up as fault codes on the scan tool that they normally use?
this is getting expensive