Heating,ac or manual

Hi all,
I have a series 3 which has been an ac car previous but I guess it has been hit in front in history and compressor,receiver dryier and hoses is gone and got ac panel still in car.
To increse or reduce heat,only way is to open bonnet and move heat valve position.
Live in Sweden so it is lot of heat adjusting.
Any advice or mayby anyone done it earlier:
Shall I get all AC parts,compressor,hoses and brackets and make AC work again or is it better to change panel inside and make it a manual heating?
Thanks for any input.
Best regards Johnny

Hi Johnny and welcome!
Check if it closes the heater vent valve in the engine bay when the engine is hot, running and the system set to full cold. Or is there a manual valve now?

Welcome to Jag-Lovers. Please post a picture of your engine bay showing the heater valve. Since your car’s heating and air conditioning system has been modified we need to see what you have now.

It is possible to have a properly operating heating system with some of the air conditioning system components removed. But those remaining components like the heater valve, as well as the A/C amplifier and assorted vacuum valves must be working properly.

Do you have the two owners (a green one and an ivory colored one) manuals that originally came with your car so that you can read up on how the heating and air conditioning system is supposed to work?


What is this “heater vent in the engine bay” that you are referring to?


Removing the AC ‘cool’ components does not in itself affect heating, Johnny - installing those components won’t do any good for your heating problem…

Basically the heater valve is operated by vacuum - but it is not used for temp regulation. Instead; a series of flaps, is positioned by vacuum, electrically or by mechanical pushrods, to maintain set cabin temps.

All air is first passed through the AC evaporator which, with AC ‘cool’ components working cools and dries the air. The flaps is then positioned to pass (or bypass) the heater core to get the air to the desired temps. Without the AC components; the system simply uses ambient air for cooling - no problems in winter, but limited cooling in summer…

The first step is to check general vacuum. Locate the vacuum reservoir, a flattened round tin some 15 cm in diameter, fitted to the engine compartment side, adjacent to the brake servo. It has one vacuum line; disconnect line, connect a vacuum gauge and start engine…

You should read manifold vacuum. Note vacuum, and turn engine off - manifold vacuum should be retained. If not; you have a leak in the system - to be addressed…

Check heater valve function. Disconnect its vacuum line tested and use the other vacuum line instead. Connecting and disconnecting vacuum; the valve should move. (It is open with vacuum applied - closed without vacuum. If there is no change; the valve might have to be replaced…

This is but the initial steps to restore normal functions - report back… :slight_smile:

xj6 85 Sov Europe (UK/NZ)

my mistake, I wanted to write „vent“ of course. Sorry.
As Frank and Paul said, with the A/C compressor disconnected the system will still function, and the coldest it will blow will be ambient temperature. Even with the heater valve open it will blow just slightly over ambient temperature air if the servo and flaps work properly.

One correction: the valve is normally open and closes when vacuum is applied. I have the line disconnected because it leaks when it closes and as there is a multitude of things wrong yet on mine so I won’t change it for now. I can still adjust air speed and temperature, so no cold feet at least.

Another check for vacuum is to simply wait a minute (more or less?) after shutdown and then disconnect the line to the vacuum reservoir and see if there was still a little left.

The system starts to work when the coolant has reached roughly 50°C, to avoid confusion.


As the others say, so should the heat work even without the cooling part itself. But this requires that the rest, for example, the vaccum, servomotor and Amplifier work. What I’m thinking of when you say “move heat valve position.” if it is the original you mean or if an extra heat valve is fitted. I have heard the term “summer valve” The original is more of the type on or off and heat / cold is controlled by flaps that Frank describes


Indeed, Janne - the servo is the central item, the physical controller of actions…

The AC amplifier controls the servo position for automatic function of the system. Crudely; the AC amp compares the readings of the temp control and the in-car sensor. The first is a resistor that varies resistance with temp setting - the latter varies resistance with cabin temps…

When their readings differ; the AC amp generates an error signal that turns the servo to the appropriate heating or cooling position. If cabin temps starts drifting off - the amp adjusts servo accordingly. Basically using fan speeds as a first recourse…

However, as system reacts to cabin temps; it’s strongly advised to use a thermometer to keep track of cabin temp when the testing out the system. If the cabin temp is below '65’F - the system will go to ‘heating’ position. And above '85’F it will start cooling. All of which may confuse issues…

Preliminary tests includes verifying proper fan speed reaction ‘Lo’ and ‘Hi’ - in ‘Auto’ the fan speed might be high or low depending on cabin temp. In ‘Def’ the fan speed should be high, and only the defrost vents should be open - in all other positions the defrost vents should be closed. This is also a crude test of general vacuum…

There is no ‘summer’ or ‘winter’ settings - the system works the same whatever the season or outside temps. The only workable modification to the system is a manual control of the servo - if the AC amplifier has failed, and isn’t replaced…

xj6 85 Sov Europe (UK/NZ)

I didn’t mean that there is a summer or winter mode by default. On my car when I bought it, they had put on an extra heat valve from an ordinary car. I guess it was because the amplifier was not working properly and therefore the servo switched to full heat all the time. That’s why I wondered what Jonny meant by “move heat valve position.”



Frank has provided an excellent overview above.

One thought, if the AC cooling circuit is not functioning, but the rest of the system works correctly…when exterior temperatures are high…using the automatic function of the amplifier will drive the servo and thus fan speeds to HIGH (Full Cooling) and likely stay in that position if ambient air is not enough to cool the interior enough to cause the servo to cycle to lower fan speeds.

If you want control over fan speeds…you may consider setting up a reversing switch to manually control the servo.



Where is (was) that extra heat valve fitted, Janne…?

In your initial post you mentioned that you had to open the hood to adjust the heater valve - why didn’t ‘they’ fit something controlled from the cabin…?) :slight_smile:

Indeed, with the system stuck in heating positions, adjusting the heater valve is one (slow and primitive) way of control cabin heating.

Given that the servo is operational, a failed AC amplifier being the only problem, manual control of the servo is fairly simple. It simply is a switch installed in the servo motor circuit to run the servo in either direction. There is even kits available to do that - but plenty of advise in the Archives on the subject.

While replacing a defective amplifier (not cheap) is the proper solution; unless the other components works as they should it’s fruitless just to control the servo…

Which is why I advise some initial testing, as mentioned, to possibly clarify state of the system as is. You need vacuum, and you need the original vacuum operated water valve - and functioning fan speeds…

Of course, fitting a push-pull cable to operate the water valve from inside the cabin is feasible - but retoring the system may be easier…:slight_smile:

xj 85 Sov Europe (UK/NZ)

Hi all,
Sorry for late reply.
Well, the valve for heating is the original controled by vaccum in center of fire wall. The car is currently not running so I can not test anything on it. If closing the heat valve is possible even without ac system,then I’saved.
It did not close on hot day but that can be due to lost vaccum or amp not working.
I will test it next time I got the car running again.
Thanks all!
Best regards Johnny

Again, here. You don’t need the valve to work for coolish air and you can close it with vacuum or by exchanging it for a manual valve (but why). The climate control does not rely on the A/C compressor to work and we assume the two control knobs in the cabin therefore do work as intended. Just not cold.

I‘d get it running first then.
Oh and I think Frank mistook Jan for Johnny but the rest is valid… so is Gary but speed can always be set to low.

The heater valve is closed by vacuum, Johnny - which is controlled by the vacuum switch on the servo…

To explain; if you track the vacuum line from the vacuum reservoir you will find a ‘T’. One line goes into the cabin through the firewall - supplying vacuum to the various AC actuators inside. One line goes down to a one-way valve which is then connected by a hose to the throttle body - providing the vacuum. The one-way valve maintains constant vacuum to the AC system when manifold vacuum varies during driving.

A vacuum hose comes from the cabin, through the firewall, connecting to the water valve - providing vacuum control of the valve by the vacuum switch on the servo.

Be aware that the AC system is not(!) designed to control cabin heat directly by opening and closing the vacuum valve. Instead the system operates in conjunction with the cooling effect of the AC evaporator (or ambient air with the AC ‘cool’ disabled) - resetting the flaps, and using water valve to temper air…

If you add another vacuum ‘T’, you can apply reservoir vacuum to the water valve - while retaining vacuum to the AC system, and the valve will now stay closed. The original vacuum line to the water valve to be disconnected and plugged - to avoid vacuum leaking.

Using imagination; you can then take a vacuum line into the cabin, and back to the water valve - using a vacuum switch to control water valve…:slight_smile:

Now, this will work to heat the cabin, sort of, if the system is stuck (or set) in the heating mode. Which roughly mean that all, or most, of the air is routed through the heater matrix. If the system is stuck in ‘cool’; the flaps directs the air past the heater core - with little effect of the water valve…

By and large; it’s probably easier to manually control the servo - which of course require that the various components is working. Which, again, warrants system checks…

As an aside; vacuum ‘generators’ are readily available - allowing testing of vacuum systems at leisure without using the engine to produce vacuum. And is useful in other contexts than the AC system as well…:slight_smile:

And to satisfy my curiosity - why isn’t the engine running…?

xj6 85 Sov Europe (UK/NZ)

It is easiest to show with an image


Clarity as only a picture can do, at times…

The heater is now “old tech” manual. The cable controlled water valve is in place of the vacuum controlled method used by the original Delanair.

I see the stubb where the AC Ranco valve one was. Gone as the AC feature is no longer present
The remaining issue is fan speed. The right knob on the console. Off, slow, auto or defrost.

My AC is inoperative. But, the heat portion works just fine. All the components are present. But, it is not charged and the power line to the compressor is not connected. I don’t want the compressor to try to compress… Out on errands, yesterday, the warm air from my Jaguar’;s heater felt nice. Spoiled as it was in the High 50’s F!!!

So, that leaves you wit the issue as to why you get no heat. When the engine is warmed up, can you feel the pipes to the valve as hot?

If so, then the “matrix” in the cabin is “plugged” up.
With a ot of luck, it might be cleansed by water or air pressure to one line opened… Ie, flush the matrix…


It may be a little confusing, but it wasn’t me who started the thread. The picture is from when I fixed my heating system. When I bought the car, the fans, the heat or the AC did not work. It’s a couple of years ago and it works like a dream ever since. It only needed some time and money :slight_smile:

Well,it was me starting this tread and I only wanted to know which would be the best way to solve a steaming hot interior can during summer. Buy all AC components to make it work or make a quick fix adding a manual valve to not melt away.
I got good answers and I know when to proceed.
To answer questions earlier in this thread:
I forced the original heat valve(in picture above) with steel thread to be in closed position to reduce heat inside car since I did not have any vaccum.
Car is standing still due to I can´t drive it out from garage and don´t want to open doors due to winter to get exhaust out.
Then I got to give the car TLC for corrosion but that is a different story…must get paint on the mk2 first.
thanks all for answers and interest.

Best regards/Johnny

change to an electronic servo control, such as this.

I would have checked why there were no vacuum, Johnny. Then rectified that as an easy fix; vacuum applied to the valve would close it. And there is plenty of vacuum available with the engine running - and straight forward to channel it to the heater valve…or try Jay’s solution…:slight_smile:

xj6 85 Sov Europe (UK/NZ)