Manual heat/AC setting

Hello, is anyone familiar with manually setting the blower direction? Currently, I have a broken servo, and the vents/defrost will only blow cold air, making me believe the blower is routing air over the evaporator rather than the heater core. Until I have time to replace the servo, I would like to force all air over the heater core and out the dash/defrost vents. I have hot water going in and out of the heater core.

Is it normal to only get the hot air out of the defrost vents? That is how my heater has always functioned.


To be clear, it is intended that all incoming air is first refrigerated via evaporater and then heated as necessary via the heater core

The servo can be unplugged and then driven (using a 9 volt battery, typically) to any operating position by applying voltage and ground to the red and purple wires. Be careful not to over-rotate the servo. (Someone here will double check me on the wire colors. I’m on my first cuppa coffee)

But, if the servo itself is non-operable, this won’t be possible. In that case you’d have to figure out a way to manually operate the flaps and hold them in the desired setting…which probably wouldn’t be that difficult

Yes. Defrost mode defaults to max heat and highest fan speed


Hi @Doug_Dwyer! You’re always a wealth of knowledge. I don’t believe I have ever achieved hot air out of the front vents. Is that normal?

Also, do you know where the flap is that would prevent heat from coming out of the vents in its current state? I haven’t seen any good diagrams on how the air routes through the climate control system.

Outboard vents at each end of the dash? When the system is in “heat” mode most of the hot air should come thru the footwell vents with a small amount coming thru the L/R dash vents.

In ‘cool’ mode most of the chilled air comes from the center dash vent, with small amounts from the L/R dash vents.

When the system is in blend mode you’ll get most of the air from the L/R dash vents. In blend mode the air will be warm-ish or cool-ish, as the system uses ‘blend’ to maintain selected cabin temp after “heat” mode or “cool” mode has done all the work, so to speak.

For this we’d need the factory service manual or the Delanair training manual…the latter of which I think someone has copied to PDF and can send it to you…if they see this thread. Either one shows the various flap locations very well. It would be difficult to describe verballly…for me, at least.

Going back to your first posting…

Can you elaborate at bit? Is the servo flat-out dead or what?


[quote=“Adam_Thompson, post:1, topic:426940, full:true”]
Currently, I have a broken servo, and the vents/defrost will only blow cold air, making me believe the blower is routing air over the evaporator rather than the heater core.

The question raised by Doug is very pertinent, Adam - is the servo actually broken. The usual problem with a stuck/non-moving servo is a failed AC amplifier…

As Doug implies; connect the red and purple at the AC amp connector with a battery. The polarity decides which way the servo motor turns. This will at least verify whether the servo operates, or not. If it does; your problem is the amplifier, and the servo can then be easily controlled - there are conversion kits for this…

The problem is that the servo controls all functions of the AC system - without turning the servo nothing actually works. In this case; cams on the servo operates pushrods to move the flaps that directs air trough, or past, the heater core. Physically turning the servo by hand, you can see the related action on the external linkages.

Which is not a practical way of controlling cabin heating - but may afford a temporary relief. If the center vents are open the servo/amplifier is stuck in ‘cold’ - and it may reset to full ‘cold’ if the AC amp is connected…

As an aside; the side vents always has the temp set by the servo/amplifier - only the flow and directions are manually controlled…

xj6 85 Sov Europe (UK/NZ)

I was able to get the servo working. It was a grounding issue. Thank you for the insights.

I have to say; the climate control system seems very cumbersome. I would love to select the vents independently of the temperature settings.

I wonder if anyone has found a solution that would give those capabilities.

When one considers this was the First Fully Automatic climate control system, well before any fully electronic magic was available, back when one had to manually open or close the heat valve with a lever and cable, and pull vents open or closed individually by hand, the fact it works as well as it does is a Marvel. And I imagine when it first hit the market it was a Stop The Presses moment!

Yes it’s a bit cumbersome, but that’s part of its charm. :grin:

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Not the first Auto Climate Control, LnrB…although the first for Jaguar, if that’s what you meant.

GM, and perhaps others, started offering auto climate control in the 60s on the higher-end models. I wanna say 1964 or so. Might’ve been earlier. They, too, could be tricky to repair.

I must say that it’s a so-called luxury feature I could live without. I don’t feel that my comfort or convenience is compromised by having to (oh my god) manually adjust the heat/ac settings :slight_smile:


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I do wonder if I could upgrade to a Bluetooth-enabled resto kit. Something like this would be cool:

The automatic vents selection is not that bad, you want heat at the lower vents, AC at the fascia vents on the console, and defrost/demist at the dash vents.
And this is what the system does.

The only problem in my books is that you get hot air from the dash vents only in defrost mode and then the system goes on full heat, very problematic on a warm rainy day.
This was my solution to this.

Other possible and easy modifications are to add switches for the AC (Napoli mod), the blower fans (Bernet mod) and the Recirculation flaps, while keeping the climate control active.

More details at the archives and in the Book.

A lot of thought went into the set-up, Adam - basically to ensure cabin comfort at all times. Designed for rapid cabin heat-up and cooling, and for stable cabin temps when reached - and working as it should; it does…so…?

All operations are directed by the servo cams, and slaved to the position of the servo. There is no problem removing the AC amplifier, eliminating the temp control, and controlling servo movement with an electric switch. But flap settings etc are still controlled by the servo - no independent control of flaps, or indeed the heater valve…

Elimination the servo for manual control of all functions will indeed be cumbersome…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

I’ll need to look at the mods @Aristides mentioned. I also have the issue where my windows fog due to rain, and AC would seem more appropriate than heat.

Indeed, Adam; the important thing with the AC is that the cold evaporator dries out the air. With the system in ‘heating’ the air is recirculated - but with rain, the screen is still cold enough (dew point) to fog up the screen with residual moisture…

In ‘Def’, wet ambient air enters and may not be adequately dried - and the cold screen cause fogging. The same applies under normal driving - to some extent it relates to screen temp. But permanent fogging is abnormal - the screen should clean up after a while…?

xj6 85 Sov Europe (UK/NZ)

It’s safe to say that for my XJ is not in the best shape. The AC is mediocre and the fan seems to only work well on high. Lastly, the wipers move at a snails speed. I switched the servo to be manually controlled with a toggle switch. All that being said, I absolutely love the car and like to use it as a everyday driver. The climate control system leaves me in a constant state of frustration. That’s why I was wondering if a total upgrade might be a fun upgrade.

Obviously the system is not working as it should, Adam - which sure will cause frustration…:slight_smile:

It may be easier to restore it to original function - a total upgrade is serious business. As an aside; the fan speeds are controlled by a bank of 4 relays, operated by microswitches. Failure of any speed may lie there…?

And on a dry screen, the wipers are indeed woefully slow!

xj6 85 Sov Europe (UK/NZ)

Maybe low on refrigerant?
In Kirby’s Book there is an extensive chapter on the AC and how to adjust the flaps for optimal performance. Worth giving it a read.

There is lots of air flow, even on low speed. It’s just that with so many outlets it’s not that apparent, and most importantly, it’s designed to be very quiet, you can’t blame it for that…

Once sorted out it works very well Adam.
And with the modifications I did, it’s perfect.

That’s a common problem.
Installing relays will transform them.
Same with the electric windows and headlights.
All the details are in the Book.

I’m not entirely clear on what you’re saying but wanted to mention that poor connections at the relay pack can cause mysterious problems.

Over the years some guys have ditched the original systems entirely and installed aftermarket. The results seem to be good, but such as job is neither cheap nor easy. It’s a big project.

The Delanair system is tricky but, personally, I wouldn’t be too anxious to dump it without first checking for the easy fixes: poor connections, a broken vacuum line, etc.


I much prefer the S1 system:
No whirring, cool air outlets to the face, individual adjustments for driver and passenger (feet….windshield) , and a simple hot and cold adjustment. The heat compensates for coolant temperature.
And a recirculation/no air lever. I tell it what to do and it does just that immediately.

Air flow is better in later cars… much better.

@Aristides - Where can I find the Kirby book you mentioned?

@davidsxj6 - I’m not sure what you mean by the S1 system.

Series 1 cars aka what was replaced by the delanair II