Preface mac to postface mac ac issuse

[dr_obson]

Hi guys

I want to change my preface macintosh HU to a postface one. I got the stereo working fine but because the postface ac controls are joined to the hu i couldnt use the preface ac controls.
It seems the postface ac contols wont actually do any controlling. the ac works but its stuck on the last setting i had it on before a swaped the units. i have found a preface pinout of the plug on the back but cant find one for postface and cant imagine why the wiring looms would be different pre to post.
Both units are single zone and there are no extra buttons on the postface unit.

Can anyone help me out here please?