Thanks again. Will get on this as time and weather permit. One clarification if you know. Most post and discussions about Delanair MkIII systems say manual operation of the system is achieved by pulling temp selector control knob out. I have a button on the ac panel upper right for manual operation of system. Is this a MkIV system that I've heard of, and if so are systems greatly different.....Can't seem to find much info about this system..Thanks again

 

There are Mk IV repair guides/manuals out there. Search this site under 'Delanair Mk IV'

The Mk IV system was used in the XJ40 sedans. Not sure if it was also used in the XJS. If nobody comes along with a definite answer you might wanna post in the XJ40 section and see if they know.

I *think* the later XJSs continued with the Mk III system right to the end....but with a string of minor changes (such as your pushbutton ) along the way.

If you look at illustrations of both the Mk III and Mk IV systems they appear fundamentally identical and some of the component part numbers are the same.

Someone will come along with a better answer.

Cheers
DD