Repair Airconditioning- S3 4.2 Sovereign

(Con Saris) #1

Hi everyone, well, a run of heat waves here has got me thinking about getting my aircon back up and running. At this stage I’m only thinking and planning and need some input from the brains trust here. So, when I got the car I knew the a/c did not work. I have since discovered a large gash in the hose from the dryer to the firewall. Don’t know how I missed it originally, but there you go. So I think its fair to say that I may need a gas top up. What are my chances that If I replace that hose, replace the dryer and gas up the system that the a/c will work? What else would I need to replace? I have read through the excellent articles here on the Delanair Mk2 system and have not started checking the actual unit but think that I will need the compressor to be doing the cooling thing first. Is that a fair assumption or can I check the Delanair unit with out cooling working? Also what is involved in replacing the hose? Is simply undo the old and replace with the new or are there special sealants or tape required?
Thanks for any feedback

(Doug Dwyer) #2

Replacing the hose is a simply remove-replace thing. The system is already empty, thanks to the gash, so no worries there.

At the firewall end the hose attaches to the expansion valve. The fitting will probably be stuck and require a lot of effort to break free. Make sure to support the expansion valve with a backing wrench. If you break the valve off your day will be ruined. Really ruined. Sealing is by o-rings. Your new hose might well come with them.

While the refrigeration portion of the system is plain-as-mud, the Delanair control system is tricky. However, even with the refrigeration side inoperative you can test the Delanair side for basic function.

With the engine running and warm, and the control set to “auto”, set the temp dial for maximum cooling. You should hear a whirring from the servo and the center dashboard outlet should open. You won’t get refrigerated air, obviously.

Now select full heating. Again you’ll hear a whir. The air output should change to the foot well vents with a small amount coming from the left-right dashboard outlets. Should be hot air, of course.

Now select defrost. Air, hot, should now go to the screen with a small amount from the left-right dashboard outlets. The fans should go to high speed and remain there.

If all these things happen the the system is understanding requests and is at least fundamentally operational. Ability to automatically keep the cabin at the requested temp setting under all conditions will have to wait until the refrigeration portion of the system is working.


(Frank Andersen) #3

Having changed the hose and receiver drier, Con - the system must be dried out before gassing up…

Applying vacuum for several minutes to the system will remove moisture - and will allow leak testing. To just fill a ‘wet’ and leaking system is pointless.

Also, original fill was Freon 12 which may no longer be available - and replacement refrigerant may requires changing some seals. Which may leak anyway after being left high and dry for some time. Personally I would leave the job to an AC shop…

The other parts of the system can be function tested as Doug describes. Lack of refrigerant will not interfere with other functions - it will just depend on ambient air for cooling…

xj6 85 Sov Europe (UK/NZ)

(Aristides Balanos) #4

As Frank says, you must also change the receiver drier.
I would ad that since you are changing one rubber hose, change both with R134a compatible hoses, get two adapters and fill the system with R134a.
Also change the O-rings at the back of the compressor and you will have a lot more chances that your system will be leak free.


(Con Saris) #5

Thanks Doug, Frank and Aristedes,
I think I needed the operational checklist for the Delanaire side of things and will get to that next weekend.
Frank I had no intention of filling the system myself, but am happy enough to do the hose and drier/receiver replacement myself. Thanks Doug for the warning about the expansion valve.
Aristedes, makes sense to change both hoses and those ‘o’ rings to negate leaks in the future. Is there a torque that the hoses should be done up to?
The heat here has been unberable at times the last month. The other week we hit 46C (114.8F) which to be honest is enough for me to seriously consider packing up and moving to cooler climes.
Not much Jaguar driving to be done with the ventilation system putting out warmish air in an already hot car.

(Con Saris) #6

Well I tried the test that Doug suggested and had little success. With the control set to auto I selected full cooling, no whir and the air stayed warm and at the footwells. Then set for full heat and the air stays at the feet and continues blowing warm air. Didn’t try defrost as the first two tests were negative. I think my problem solving will have to be sorting vacuum to the unit. I know that there are vacuum hoses under the bonnet that are not connected to anything, that is going to have to be my first priority. One question though, can I connect the a/c vacuum hose directly to the manifold or do I need to connect it to the vacuum resevoir?

(Doug Dwyer) #7

For the moment forget the possibility of vacuum issues. Those can be faced later, if needed.

“No whir” means the servo is not operating. Making the servo operate is step one. In this system, briefly, the amplifier is the brain of the system and the servo is the mechanical robot that operates the flaps, switches, and vacuum controls. The servo takes commands from the amplifier.

First check all 4 fuses.
-One on the amplifier ground wire, behind the console cheek panel, left side

-One behind the right side cheek panel, clipped to the heater case, on brown and yellow wires

-One in RH fuse box

-One in LH fuse box

Don’t forget the clean the fuse clips/contacts. They’re often corroded.

If the servo still doesn’t whir with good fuses and clean contacts we’ll keep digging


(Foggyoo) #8

You may find a small filter on the vacuum feed, this can be clogged.

(Doug Dwyer) #9

When replacing fuses this might be helpful, unless you have a ready supply of Lucas fuses


(Con Saris) #10

Thanks Doug and Foggyoo maybe another week before I get to this but I’ll keep you posted.

(Gary Crosby 75 XJ6L, 85 XJ-S, 09 XF Supercharged.) #11


The AC system must have power and a working servo. Both tests can be conducted from the left transmission tunnel cheek panel.

I recommend testing as follows. Remove left trans tunnel vent panel. Separate the white octagonal amplifier plug. Insert a pin into the plug socket for the brown wire…a large paper clip works well. With a multi meter check for 12 volts on the brown wire with ignition on and AC system set to auto. No voltage indicates either bad power fuse or failed system power switch in mode control. If you have 12 volts…proceed to testing the servo.

To test servo…insert pins into the red and purple wires of harness connector. With a power source ( 9 volt battery with clip leads works well) apply positive to red and negative to purple…listen for servo whir. If no response, servo could be at limit switch…so reverse the leads…positive to purple and negative to red…listen for whir. If no response from servo…servo is defective and will need replacement. If servo is responsive and whirs…failure of the amplifier is highly suggested.

As Doug notes.
Fuse in LH panel is main sensing system power
Fuse in RH panel is power to high current fan circuit
Fuse in left cheek panel inline ground wire is to amplifier
Fuse on right side of heater box is power to compressor circuit ahead of ranco thermostat.

Hope this helps



(Con Saris) #12

Thanks for that Gary, more things to check out. Are the sides you mention the same for left and right hand drive cars? Makes me wonder when I bought the car I found 5 packs of fuses in the center consol. I think the PO may have been chasing the same problem. Still I have plenty of time and am in no rush and am aiming to have this fixed by next summer (DEC).

(Frank Andersen) #13

There are plenty of good reasons to have assorted fuses available, Con…

…the AC takes 15A, which on LHD is in the aux fuse box. The amp ground fuse mentioned by Doug a 3A inline fuse - and sometimes an inline fuse to the compressor clutch.

The compressor should engage whenever the switch is out of ‘off’ - signifying that the amp has power. Which is also indicated if the fan speeds, ‘Hi’ and ‘Lo’, functions.

No servo action must be pursued, and Gary’s suggestion of testing the servo will eliminate that as a reason - leaving the AC amp as a prime suspect…

Without refrigerant, the system depends on ambient air for cooling, but heating will work in cold weather - unregulated if the servo doesn’t move. That the centre vents do not open means the system is in ‘heating’ mode - and vent outlet air temp will likely be higher than ambient…

Check defrost air flow; vents are held closed by vacuum in all positions but ‘Def’ - if so; system has vacuum, though vacuum issues can be pursued later. As Dough says; the serve must move, indicating a working AC amp.

Without a working amp/turning servo; other system faults can not be effectively pursued…

xj6 85 Sov Europe (UK/NZ)

(Gary Crosby 75 XJ6L, 85 XJ-S, 09 XF Supercharged.) #14


I would caution using a 3 amp fuse in the amplifier ground. The Australian “shotgun shell” style amplifier which was available from Caufield Jaguar some years ago uses components with a maximum rating of 1.5 amps. Over fusing of the amp will cause the failure of the internal component, causing it to crack and melt.

I personally ship all of my replacement amplifiers with a 1 amp fast acting fuse. This rating is more than adequate for a properly functioning amplifier /servo circuit and protects the expensive amplifier.

I routinely find servos that have high amperage draw due in large part to thick gummy old grease on the gear mechanism in the servo.

Just a thought



(Frank Andersen) #15

I don’t disagree, Gary…

xj6 85 Sov Europe (UK/NZ)

(Con Saris) #16

Hello all,
I’ve just finished checking out the things suggested above and here are my findings
I have found and checked the fuses. all were good except the one in the RHS cheek. This one is a 10amp fuse and goes to the compressor. It had blown. I replaced it with another lucas fuse that I cleaned and checked with a multimeter.
all the others were good.
I checked the power to the brown wire in the octagonal plug. This gave 13.6 volts so am thinking that’s ok.
Next, applied power to the red and purple wires, no servo action. Reversed polarity, still no servo. So I am guessing that the servo is dead. Need to start studying removal I guess. And I suppose this still does not eliminate the amp from the list of damaged parts!

By the way does anyone recognise this part? When I removed the LH cheek it dropped out. It’s made of plastic that flexs fairly easily. Maybe its not even a part from this car?
Thanks again for all the help so far

(Gary Crosby 75 XJ6L, 85 XJ-S, 09 XF Supercharged.) #17


Applying power to servo with no response does imply a faulty servo…or bad pin contact in the wiring harness plug. My next course of action before removal of the servo is to move to the right hand cheek panel and find the white octagonal plug for the servo. 11 or 13 pins. Disconnect and perform the same power test at the servo plug. Red positive - purple negative and then reverse polarity. If the servo now runs…then the plug connection is suspect and typically repaired by using a small pick or jewellers screwdriver to pinch the female plug barrel together. If the servo still does not operate…removal of servo is necessary.

Servo removal: 1. remove RH cheek panel. 2. Remove vent extension by removing 3-4 pozidrive screws. 3. Mark the position of flap rods against retaining arm fixture to ease reinstallation. 4. Servo is held by 8mm nut inside of heater box accessed thru vent opening. 5. Using small flat bar or screwdriver separate foam mounting tape mounting by prying the servo from the bottom of heater box. Note there is a short alignment stud on mounting face of heater box which may require gentle pressure to clear servo assembly. 6. Disconnect white octagonal plug and vacuum lines, and remove servo.

Grease on servo gear train can become quite thick and tar like…cellulose thinner works well to clean with soft brush.

Warning: I don’t recommend removal of the feedback potentiometer on forward side of servo. But if necessary…only remove feedback potentiometer after carefully marking its orientation and clocking its position. Failure to position the feedback pot in the correct position could result in damage of the cam mechanism or inaccurate climate control system operation.

While an amplifier cannot be ruled out as of yet…you must have an operational servo before further evaluating the system.

Please note…I have encountered a rare servo which mounts with 4 screws (2 from backside) into the side of heater box…if this type of servo is found…the only method of removal is to extract the entire climate control system and dashboard. This has only been found on early XJS and 1 Daimler thus far.

That plastic part looks like a fin from the cheek panel vent.?

Hope this helps



(Con Saris) #18

Gary should I reconnect the other Octagonal plug?

(Frank Andersen) #19

Not necessarily, Con - the plug nearest the servo connects directly to the servo…

A working servo is required even if you bypass the AC amp and ‘go manual’…

It’s not common for the servo to fail - so some contact cleaning as suggested by Gary is certainly pertinent…

xj6 85 Sov Europe (UK/NZ)

xj6 85 Sov Europe (UK/NZ)

(Aristides Balanos) #20


You have to remove the servo as Gary says and bench test it.
It’s not that hard, and a good opportunity to check everything, including all the vacuum valves.
Kirby’s book has all the info on how to readjust all the rods.

To add to Gary’s comments, there are a couple of diodes besides the motor that in my servo had gone bad.