The saga continues, after taking the car to the mechanic he has found the following:
1 - If you manually power the green-grey cable on Pin ?? (Will update when I have the car) the regulator valve opens and cools the cabin.
2 - He has a donor car that he tried swapping AC Heads and it seems my OG unit and the replacement I bought both work on the donor car but the reverse does not.
3 - The mental bill as to how much this is going to cost keeps rocketing up in my mind.
I'll keep you all appraised and hopefully remove someone's headache in the future...