Diagnosis should start with a good service manual (preferably factory), and a good understanding of HOW the system operates. Odds are the climate control has a 'self-diagnostic' mode it can be put into to help narrow down the area of the fault. Otherwise individual component and circuit testing will need to be done.
I'm honestly shocked(in a good way!) that you have the factory service manual.(It is 'service manual' not 'owners manual', correct?) I'm used to Honda manuals and Hondas on-line info at work ,I'm sure Jaguar has their manuals set up differently. Do they still have the hood listed as the 'bonnet'? I've seen some old MG manuals and they certainly weren't 'American friendly' as far as terminology goes.Do they have the heating and ventilation seperate from A/C? If so then maybe the test procedures for the blower motor circuit (interior front fan?) will be outlined in that. Maybe If we are both lucky, someone out there can shed some brighter light on the 'use' of the manual. Probably at this point the most I can do is make stupid remarks , just for entertainment purposes....Gotta have fun while your car's pissing you off ...right??....Good luck. If I can actually be of any more help I'll try my best , just ask.