XJS heat thru center?

Hello, does anyone have a way to get heat thru the center vent?

Hi Robert and welcome.

You would have to modify the vacuum line so that the center vent opens all the time. (the center actuator on the diagram)

But why would you want to do that though?
Heat rises, you want it down, not up.

Hi, thank you for your reply. It is not so much I want the heat thru the center it is I do not want cold air blowing in my face. Is there a way to stop air flow thru the center?

I see that you are new to Jag-Lovers. Welcome.
Some of us have removed the original fixed center vent in our XJ-S and replaced it with one from an XJ40 that directs the air, after trimming the XJ40 vent a bit. I made this modification to my wife’s 1990 XJ-S convertible. You will find lots about this in the archives by searching for “center vent”.


Hi Paul, thanks for responding. I will try to locate one . I don’t understand the logic of cold air
blowing out when heat is selected. Good thing I put it away for the winter I guess. Thanks again…

Now you guys have me curious - don’t we have heat out the center vent (whenever desired) on our face-lift models? :confused:

Cold air is not supposed to blow out of the center vent with the heat on. If it does then you have a malfunction somewhere.
What is the history of the car? Did you recently purchase it and it had this problem when you got it? Or have you had this car a while and it worked properly for you but it just recently started acting up?
The archives are a gold mine of information about almost every malfunction or failure. If you search the archives for “center vent” you will immediately find lots of posts that will help you see what others have experienced and how they fixed their problem.


Robert’s profile shows that he has a 1989 XJ-S and my answer is applicable to the pre-facelift cars. I have no clue about how the face-lift cars work and more often than not they seem to be different from the earlier cars.


Hi , this is my third XJS ( stuck on them) and they have all been the same. I read some where the Brits designed it with cool air in the center because warm air in face puts you to sleep. What is a face lift car?

No, as Paul said, there is something wrong.
You center flap should be closed on heat mode.
If your system otherwise works as it should, it’s, most probably, either that the center vent is stuck open or the vacuum switch is broken (vacuum = vent open)
Does the vent closes when you turn the climate control off?

On my ‘88, when set to auto mode, when system is heating there is no airflow through the center vent; as cabin reaches set temperature air will flow through the center vent. Are you operating the system in “manual” mode (temp knob pulled out)? If you are and the ambient is higher than set temperature it blows through dash center vent, indefinitely from what I can tell. Also, if the a/c system isn’t cooling fully, it may continue to blow through center vent because cabin isn’t cooling enough.
Also, the dial at the bottom (face level temp) will vary the center vent from slightly cooler to slightly warmer than outer dash/floor outlets.

You should disconnect the main vacuum line that feeds the climate control ( at the engine bay after the one way valve) and see if the vent is closed or not. If it does close then the problem is the switch at the servo unit.

That’s what I also thought when I first got the car and nothing was working right… But now that it’s fixed it’ works very well and really adds to the comfort and luxury feel of the car.
Don’t forget that this is 70’s technology and fully automatic climate control is a feature that only lately became common (electronics helped a lot…).

I think that there is a procedure in Kirby Palm’s book to cycle the flap with a 9V battery and then leave it disconnected…if I recall it is a drum driven by an electric motor. If there is no airflow when the system is turned off, sounds like a sensor/amplifier issue- you could disconnect the flap/drum motor with the system off and it should stay directed to the floor. Easily reversed if it doesn’t shut off the airflow.

There’s also a linkage adjustment procedure in the Book. I dunno what the status is on the average Jaguar, but on my '83 things started working a lot better after adjusting that linkage.

Hi Aristides, I did disconnect the vacuum line that feeds the climate control and the center flap does close. Where is the switch located on the servo?

In order to access the switch the servo assembly has to be removed.
It’s done from the right side foot-well. It’s only two screws, but you will have to undo all the linkage and vacuum connections.
Take notes and follow Kirbert’s adjustment procedure on reassembly.
I don’t know how easy, or even possible, it is to repair the switch as I have never done it.
Fellow lister David Boger is a good source to get a replacement part if needed.

An alternative solution would be to find a generic vacuum switch, intercept the line and have the flap open and close with a toggle switch mounted somewhere on the center console or dashboard.

You can find more info here:

His profile says he has an '89, so he has the MkIII
Delanair, not the MkII. I’m not sure how much difference there is for this particular control, but overall control of the system is considerably different.

Ah, that exotic MKIII…
Yes I wonder too about the differences.
Doesn’t it also have a servo unit?

Here’s the MkIII manual.Delanair MKIII Introduction.pdf (1.1 MB)

Mk III? Sorry I didn’t notice that. There’s a 95% chance that the symptoms are caused by one of the two servo motors failing. And there’s a 100% chance it’s the one that’s a PITA to get to.