This is what has been done, so far:
New condenser and dryer (obtained under guarantee from where I bought the car)
Compressor clutch works, when over-ridden
New low pressure switch on front pipe. The original one showed short-circuit, and I believe this might have caused problems elsewhere.
System fully gassed and up to pressure.

I have reclaimed the car from the Jaguar specialists, who are very good, but right now are stumped (they have completed a load of other work for me) and they want me to return it to them on Monday. Meanwhile, they believe there is likely to be a wiring fault with shorting somewhere in the loom, but seemingly their wiring diagram does not exactly follow my own model. I believe they tried to bypass the earth and low voltage live, but that did not resolve the issue.

Despite all of their work, the aircon does not work. Has anyone any ideas how to proceed on this? Any pointers I could pass on to them might save me a bundle of workshop money!

 

Have you interrogated the climate control unit for trouble codes? That might at least point you in the right direction. Worked wonders for me.

 

I think that would have been done, but will ask the question on Monday.

They feel that there is an extra feed to the unit from somewhere, not shown on the wiring diagram. This is a late model x100 - could be very helpful if there is a diagram showing any changes that would have been made.

 

http://www.jagrepair.com/images/Auto.../jagxk2003.pdf

The above covers your car.

 

Two wires between the switch and the ecu were bypassed, since it seems they had a short; the switch itself was also replaced. When this happened the ic 'lit up like a christmas tree'. The engineers tried a temporary replacement for the ecu, but this made no difference.

Their current thinking is that there is another feed to elsewhere, probably from the live low voltage feed between switch and ecu, but that feed does not appear on the 2003 circuit diagram - so by bypassing the original wires they altered things in other parts of the system. They are competent guys, but right now are stumped.

So if the combined might of forum expertise can suggest any pointers I will be most grateful, especially as we are about to go onholiday to Portugal where it is around 40 degrees C (105F) right now!

 

It has turned out to be my instrument cluster!! For a bit of a history of this self-generated horrible nightmare, have a look at some of my other posts......

There is a range of possible causes. The pressure switch was faulty. When that switch was replaced by a new one, the system still did not work at all - but by that time, it might have damaged the replacement cluster.

So enter the latest one, cluster no.3 - see later. With the new pressure switch, it worked.

This is my analysis.

The fault I caused on my original instrument cluster, no.1, might have damaged the pressure switch. That faulty pressure switch subsequently damaged the replacement cluster, no.2. With a new pressures switch and new cluster, all was well.

or: the faulty pressure switch was nothing to do with my original damaging of cluster no 1, but it did damage cluster no. 2

or: the replacement cluster, no.2, was also faulty.

or: cluster no. 2 did not have exactly the same reference as cluster no. 1, whereas cluster no. 3 did have exactly the same reference as the first one, so it might have been a mismatch problem.

My belief is that it will be the first or second of the above points that was the culprit. Now happy and cool!

 

2003 on and the A/C control electronics changed. The IC became part of the loop, and the CAN signal for the clutch to engage originates there.
An earlier IC just wouldn't know what to do...

Glad you got there