Ok, I have confirmed that the PS switch is involved in the AC clutch control in the 2.2L S10 just as FAST355 has stated.

So my hurdle at the moment is to get the PCM to recognise the PS switch opening and closing. At the moment this input (pin F8) is configured somewhere in the .bin as the 4WD Low Range input.
When I select 'PS Switch enabled' in the bin, grounding F8 still toggles 4WD Low in the ALDL scan.
I haven't been able to find anything in the hac document to determine what else it want to see it as a PS switch input.

Any clues?
Thanks to those who have contributed :)