My climate control is not operational alright. With ambient temperatures exceeding 97° F here driving with heat on is not enjoyable, I can tell you right now.
I did my homework. Palm's Book, some other documents. However, some rather simple questions need answers.
They mention vacuum check valve in Kirby's book. Can some kind soul tell me where is it? I do see a big one in engine compartment, but I don't see any vacuum hoses going to the AC control unit from it. So the second question would be: where from the climate control gets its vacuum?

 

Find the vacuum reservoir and make sure the hoses are attached. I can't remember where it is on an XJS, but someone here will know

https://www.jaguarclassicparts.com/u...tank-and-hoses

The check valve will probably be found between the engine and the firewall, RH side, just aft of the cam cover. In that neck o' the woods, at least.

Make sure you don't have vacuum hoses dangling where they enter the cabin to supply the climate control unit. As I recall this is also on the RH side in the area of the footwell

Cheers
DD

 

When you set the system to 'Auto" and slowly turn the temp selector dial, do you hear a slight humming sound from the servo? You should. If not, finding out why is step one.

Could you be a bit more specific as to what is (or isn't) happening with the system?

Cheers
DD

 

Thanks for replies. It may be there is no power to it. I do not hear the servo. I just thought I have to start somewhere, so I started with vacuum lines. I found the check valve and it is OK. Now, according to the picture there has to be a tank somewhere ...
But sure enough, electrical part needs attention. The damn thing has 4 fuses, gotta find them.

 

Update, that fusebox is a POS. Ordered a better one, for modern fuses.

 

Two of the fuses should be in the main fuse panel under the dash, LH side

Another fuse will be behind the console RH side "cheek panel", clipped to the side of the main HVAC case, on brown-brown/yellow wires

The fourth fuse will be on the amplifier ground wire, behind the console LH cheek panel

Replace the existing fuse panel as you wish but in the meantime make sure the end caps of the existing fuses are shiny clean...as well as the clips that grip them.

Cheers
DD

 

If you need to replace fuses this might be helpful

Fuse Conversion Chart

Cheers
DD

 

The vac reservoir is under a plate where the pedals would be if your car had the driver on the opposite side, There is a vac tube from the manifold to the reservoir with a non-return valve in it. the valve may be jammed or the tube may be perished. Another tube goes from this reservoir TO the cabin unit, again it may not be sound.
The most likely problem in the cabin unit is either the amplifier or the servo or both not working. the solution is to contact Gary Crosby at JagAire (in the USA) and he will supply test data and new parts as required.

 

Thanks. Unfortunately he has no web page. The only search result points to Facebook, and this is the place where I do not go.

 

Try this:

https://www.jag-aire.com/