Jaguar XJ-S. Manual - part 125

 
 

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Remove the C-clip from the shaft, and remove the stack of washers against the front bearing; be sure to keep track of 
the washers and the order they are installed in.  Turn the shaft and observe the front bearing, which should remain 
motionless within the housing.  If the bearing turns with the shaft, a positive anti-rotation modification is called for.  
One method is to drill a hole through the steel housing and into the bronze bearing and install a tiny self-tapping screw. 
 Make sure the tip of the screw doesn’t contact the shaft itself, and that the head doesn’t interfere with the C-clip and 
washers. 

Pull the little covers off the brushes and remove them.  If they are too short, replace them; don’t bother trying to find 
original Jaguar brushes, just find some slightly larger at a motor or vacuum cleaner shop and file them down to size. 

While the brushes are out, use a VOM to check the continuity at the segments of the commutator.  There should be 
some form of continuity between any two segments you test.  If you find a segment that doesn’t seem to connect to 
anything, you’re in trouble.  If you can see why (a winding disconnected or some such) you can decide for yourself if 
it’s possible to fix.  Don’t use any solder, it won’t take the heat, connections must be made mechanically or by tack 
welding. 

If you’re like me, you’ll grind a small flat on the shaft for the setscrew in the impeller.  I just don’t like setscrews on a 
plain shaft. 

Before reassembly, inspect the condition of the three rubber mounts.  If they are dry and hard or crumbling, renew or 
fashion suitable replacements from grommets, hose, whatever. 

If your blower fans are toast, Vicarage (see page 702) carries replacements at reasonable prices. 

 

BLOWER FANS - REINSTALLATION:  The rubber duct may be a neat feature, but it can be a real pain to reinstall.  
To make life easier, attach the duct securely to the blower assembly before installation.  I suggest the use of aluminum 
tape. 

 

VACUUM:  The control system relies on a supply of vacuum from the engine, and stored in a reservoir.  As Tom 
Wagner discovered, it pays to make sure the supply is working before troubleshooting the rest of the control system.  
There is a check valve in the line to allow the reservoir to hold vacuum when the throttle is opened, and this check 
valve stuck shut -- preventing either the reservoir or the control system from getting any vacuum. 

 

VACUUM CHECK VALVE:  One might expect that the normal failure of the vacuum check valve is that it fails open, 
but Mike Morrin had the opposite problem.  “My A/C system has always had marginal performance of the vacuum 
actuators, with the heater valve (new) and centre vent flaps always slow to operate.  I got tired of the centre vent taking 
5 to 20 minutes to open. 

“Tonight I decided to check the vacuum non-return valve, which seemed to be working.  While trying to decide what to 
do next, I was sucking on the non-return valve, and it occurred to me that I was sucking rather hard before any air got 
through. 

“On impulse I tried to pull the valve apart to see what was inside, but it was too tight (or glued together).  I then poked a 
piece of steel wire in the end where the air goes in, and there was a small click.  That must have been the rubber thingy 
unsticking from its seat, because the valve is now much easier to suck through (but only one way).  After refitting, all 
the vacuum actuators are now working like clockwork. 

“That is the easiest repair this week. 

“The XJ-S help book mentions that these valves sometimes block up completely, but this was only partial, and seems to 
have been fixed by a poke in the eye with a blunt stick.” 

 

 
 

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CENTER VENT:  The center dash vent on most XJ-S’s has three sections: a section on the left and right ends that can 
be adjusted to aim where desired, and a center section with no adjustability that simply blows straight rearward.  Here 
in Florida where the weather is both hot and humid, this center portion can blow enough cold air straight back to cause 
the rear windshield to fog up -- which is a real pain, because the rear window defroster has a timer and won’t stay on 
indefinitely, you have to keep turning it on and off to maintain visibility in the mirror!  Those who don’t have fogging 
problems still dislike that center vent blowing air to the rear, since only sadists ask anyone to actually sit in that rear 
seat.  Peter Cohen confesses, “Over the years, I have developed the unconscious habit of driving with my elbow resting 
on the console, arm up, and my hand positioned as a diverter to direct the cool air toward me.” 

Emile A. Des Roches suggests two possible fixes:  “The Cheap Solution -- Lift off the surrounding wood (gently); the 
plastic vent will come out with gentle even pressure.  Cut a piece of relatively stiff black cardboard to the height of the 
inside (towards inside of dash) vent and to a width roughly 2” narrower than the width of the center vent.  Place same 
(black side facing cockpit) in the vent and reassemble.  This solution performs the same function as resting one’s hand 
in the air to divert air towards the driver and is far more sanitary.” 

This author made a similar modification to his center vent, except he used black plastic instead of cardboard and shaped 
it into a V so it would more definitely deflect the air to the sides.  Using the simple flat piece may cause more blockage 
rather than deflection -- which may be desirable since it would result in more air flowing out all the other vents. 

To all this, Franck Guilloteau adds:  “While my car is an ’85, the wood trim is in immaculate condition and I found that 
after several unsuccessful tries it wasn’t worth the risk of breaking or chipping the trim.  I resorted to an alternative 
method of removing the two directional vents of the main center vent.  A small screwdriver, X-acto blade and minimum 
dexterity will do the job in five minutes.  Directional vents have a small leaf spring that increase the friction and hold 
them in place; it can be pushed out prior to removing the vent.  These openings allowed me to slide black cardboard (or 
plexiglass covered with black felt in my case) and wedge it in place from behind.  All told a really “cool” mod.” 

Des Roches continues:  “The More Problematic Solution -- Replace the center vent with one from a very late XJS.  At 
some point after 1993, the center vent design with moveable vanes at the edges and fixed vents at center was replaced 
with a design that consists of two (no space between) adjustable vents.  This is a direct (no trimming) replacement for 
the earlier unit which presumably could be obtained from either Jaguar spares or a wrecking yard.”  Dean Gosselin adds 
that the part part no. is BEC-26361. 

Dan Jensen adds, “I changed out the center vent on my XJ-S... It makes a dramatic difference in the amount of cold air 
that can be directed over the driver and/or passenger.  I would offer one additional note to the installation instructions.  
While the replacement vent has the same width and height as the original in my car, it was approximately 1/8 in. 
deeper.  The extra depth resulted in the vent face extending out a comparable distance from the metal dashboard and 
prevented the wood fascia from sitting firmly against the dash.  As a result, I had to get out a wood rasp and file off 1/8 
in. around the inner perimeter of the vent.  This took about 15-20 minutes, including the time needed to get all the little 
specs of plastic off the louvers when I was finished.  In addition, it was necessary to file two small central notches in the 
metal dash to accommodate two added bulges in the new vent.  This took no more than a minute or two with small 
round file.” 

Samuel Louw provides an incredibly detailed description of this job, in response to the concerns that many people had 
about damaging their wood trim:  “It is really simple and you don’t have to be an engineering genius to be able to do 
this.  The most scary part is actually to remove the wooden center fascia, since this holds the vent in its place.  It really 
sits tight.  There are four metal springloaded pins that are attached to the backside of the fascia and are pushed into four 
holes which are in the metal dash plate behind the nice wooden fascia.  When the fascia is replaced, the four metal pins 
are pushed into their holes and the springloaded clips are compressed, not in the direction of the pushing action but by 
the sides of the holes, since the clips are V-shaped.  Now when you want to remove the fascia, you first have to 
overcome this spring action. Since you think the fascia is waferthin and will break, you might want to give up, but that 
piece of wooden fascia is almost 8mm thick in places.  You have to open the glove compartment and slide the blade of 
typically a steel table knife underneath the fascia.  Then you must start wedging it away from the dash.  The right side 
steel pins are app 5mm away from the top and bottom of the fascia and app 35mm in from the glove box side from 
where you will be wedging.  The left side bottom pin is also app 35mm from side, but the top pin is app 70mm from the 
side and in the area where the fascia is only about 13mm wide.  Be careful of breaking the wood there.  I hope that by 
knowing beforehand how things look at the back it will make you more comfortable to do the job. 

 
 

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“The new vent has four small plastic flanges with holes in it, two per side along the two long horizontal sides of the 
vent.  The flanges are about 10mm x 10mm.  They have to be removed, since the pre-’93 cars do not have holes 
through which the vent is fixed in position.  This is definitely not needed, since the vent is held in position by the center 
piece of wooden facia, and that really sits tight.  So, you have to remove those flanges (can be broken off carefully with 
normal pair of pliers) and then just file the leftover away. 

“The other small job is also due to a small difference on the new vent, but again, this is small and easy to do.  The new 
vent has has two small D-shaped bulges on both sides. This will most probably interfere with the metal plate of the dash 
where you have to push in the vent.  Just mark the position of those bulges and file away the notches in the metal plate 
(About 5mm wide and 3mm deep and halfround shape; use small round file). 

“I did not notice the problem of the new vent being deeper than the original, as was noted by Dan Jensen. Thus I did 
not have to do that filing to make it less deep.  My new vent pushed in all the way until it settled against the rectangular 
sponge seal and there was no interference with the wooden fascia due to a bit of vent protruding.  If you do find this 
problem, just file away the required amount from the rear of the vent. 

“The correct Jaguar part no for the new vent is BEC26361.  Do remember to buy the new foam seal as well.  You are 
not likely to save the old seal, as it will have rotted and deformed. 

“You will have complete control over the direction of air flow both up and down and to the sides.  If you live in an area 
with hot weather as I do, it is essential.  You won’t believe the difference.” 

 

AIR CONDITIONER COMPRESSOR:  Up through 1992, the Jaguar A/C compressor was labelled “Harrison” but was 
in fact the standard GM item referred to as an A-6 -- and therefore comparatively cheap to replace.  In fact, it is 
generally recommended to simply replace the compressor rather than attempt even the simplest repairs.  After a few 
years, the O-rings start to fail, and each time you correct a leak you must have the system evacuated and recharged.  
With the current regulations on R-12 refrigerant, the cost of a single charge can exceed the cost of the compressor.  If 
you are having the system recharged anyway and the compressor is more than seven or eight years old, it might be wise 
to simply replace it even when it is still working fine. 

Although you can find an A-6 compressor really cheap, Randy Wilson says, “The compressors should be good for 
many years.  Continuous failures are not the fault of them being rebuilt units.  It’s the fault of them being cheap quasi-
rebuilt units.  This is a fairly major problem we fight in the auto industry.  I can buy these A-6 compressors from a local 
distributor for $49 per unit in very small lots... with no core return.  These units, I can tell you from experience, have an 
average life expectancy of around a month.  Many fail the first day.  I have found a rebuilt compressor that I like.  It’s a 
lot more expensive.  But I haven’t had one of them fail yet.” 

James Teston describes a quality rebuilt compressor:  “There should have been a nitrogen charge under pressure in the 
compressor that gave off a distinctive hiss when you loosened the cover plate.  This is to prove to the installer that the 
unit is 100% leak proof.  Kind of like the tin vacuum safety lid on grocery jars in reverse.” 

Before selecting a rebuilt compressor, read about the clutch below. 

The threads on the replacement compressor are likely to differ from the original, in which case you will have to replace 
the mounting bolts.  In particular, the two mounting bolts at the bottom rear and the long bolt that holds the inlet and 
outlet connections in place are 10mm on the OEM compressor and may have to be replaced with 3/8” bolts (either fine 
or coarse, they vary) when installing a replacement.  3/8” is only slightly smaller than 10mm, so sleeving will not be 
necessary.  Also, the small front mounting bolts are 8mm x 1.0 (metric fine thread) and may have to be replaced with 
5/16”. 

Aggravating the thread situation is the fact that rebuilt compressors tend to be delivered with the threads all boogered 
up, and covered with paint besides.  This makes it difficult to tell which thread it is, since no bolt wants to thread into it. 
 It’s no fun getting to these bolts when they’re down in the vee, so you’re advised to determine what threads they are 
while the compressor is on the bench and to chase the threads with a tap so the bolts go in easily. 

The new A-6 compressor also may not fit the protection switch that was in the original compressor.  Read the section 
on the COMPRESSOR PROTECTION CIRCUIT on page 502. 

 
 

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The A-6 compressor is supposed to have a pressure relief valve screwed into the back end.  If the rebuilt you get 
happens to have a plug in its place, transfer the pressure relief valve over from the old compressor.  If the thread isn’t 
right, Peter Havas suggests you just swap out the entire rear plate of the compressor!  The XJ-S has a history of 
problems getting enough air through the condenser/radiator to keep the high side pressures down, so this is one car that 
really needs to have that pressure relief valve in place. 

From 1993 on, a Sanden compressor was used.  While many may bemoan the discontinuation of the excellent A-6, the 
Sanden likewise has an excellent reputation among A/C mechanics.  Note that fitting a Sanden to an earlier car would 
probably require replacing the hood as well; the later hoods have a different shape primarily to accommodate the AJ6 
engine, but they allow room for a larger diameter compressor on the V12 as well. 

 

COMPRESSOR RELOCATION/SUBSTITUTION:  Many owners feel it’s worthwhile to try to replace the all-iron A-
6 compressor with some other compressor that weighs less -- for example, the Sanden used on the later models.  
Obviously hood clearance is an issue -- unless the compressor is relocated around the side of the engine. 

The capacity of a compressor is generally described in terms of the number of cc’s it moves per revolution.  If you want 
to compare the capacity of one compressor installation vs. another, you need to compare the cc’s per revolution and the 
relative sizes of the pulleys in the belt drive.  If you install a compressor with the same cc’s per revolution but a larger 
pulley, the capacity will be decreased because the compressor is turning slower.  Conversely, you may be able to 
achieve adequate capacity from a smaller compressor by putting a smaller pulley on it -- or a bigger pulley on the crank, 
which may be easier -- to turn the compressor faster.  You must be careful not to overspeed the compressor before the 
engine reaches redline, though. 

All that said, one must suggest that the A-6 is probably oversized for this application.  The system is rated at around 2 
tons, but the compressor isn’t likely to be the limiting factor; it’s limited by the size of the evaporator and the ductwork. 
 Even if you installed a compressor that moves far less freon at a given engine speed, you’re not likely to notice the 
difference except perhaps at idle. 

There is a minor concern about relocating the compressor to a lower location.  Having the compressor up high -- 
especially above that hot engine -- has the advantage that it will prevent liquid freon from pooling within the 
compressor while the car is parked and then causing a compressor lock on startup.  Compressors in household air 
conditioners generally have a “sump heater” in them that prevents freon from condensing in that location.  It evidently 
isn’t a great concern in automobiles, because many come from the factory with the compressor mounted low.  Since the 
condenser is likely to always cool down faster than the engine and the compressor, perhaps the problem is avoided.  
Perhaps the compressors mounted low are designed that they’ll just push liquid into the high pressure line rather than 
trying to compress it. 

In whichever case, it’s always a good idea to route the high pressure line so that it goes up high and then back 
downward to get into the condenser.  This prevents liquid in the condenser from draining back into the compressor 
while the car is parked. 

It’s also a good idea to have an electric fan that runs on after the engine is shut off.  Besides addressing heat soak in the 
engine, it helps to cool off the condenser quickly and causes the freon to condense and pool there rather than in the 
other parts of the system. 

 

COMPRESSOR CLUTCH:  The assembly built onto the nose of the compressor is the clutch, the system that engages 
or disengages the drive as the climate control system calls for cooling.  When disengaged, the compressor is nothing 
more than an idler pulley.  When engaged, the drive plate on the very front of the compressor is turning with the pulley, 
making it very easy to visually confirm operation.  If the engine is not running, you can still confirm operation; when 
the clutch is disengaged, you can turn the drive plate fairly easily, turning the compressor.  When engaged, you can’t 
turn the compressor by hand because it’s locked to the belt drive, you’d have to turn the engine. 

The clutch is magnetic.  Under the pulley is a coil that is energized when engagement is called for.  This magnetizes the 
pulley.  The drive plate contains a rubber isolator to absorb vibration and also features three straps riveted at one end to