Jaguar XJ-S. Manual - part 133

 
 

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You will need a device to connect the cans of oil and refrigerant to the low side service port in order to charge it -- and 
you can’t use the charging equipment that you used with R-12 because both the cans and the low side service ports are 
different with R-134a.  Cans of R-134a have a little threaded nipple on top to connect to. 

With R-134a, one basic setup is a brass valve that screws onto the top of the can with a little spike that punches a hole 
into the top of the can, and a short length of hose with an R-134a-standard threaded end that attaches to this valve and a 
brass quick-disconnect on the other end to connect to the service port. 

There’s also a similar device made entirely of plastic. 

There is a device that attaches directly to the can and you turn the can over and jam it down onto the quick-disconnect 
port.  No hose, no valve.  I suspect you are not supposed to use this type to put refrigerant in the system, since you 
could easily introduce liquid refrigerant into the low pressure port.  It appears that this type is chiefly used for such 
things as adding dyes or sealers to the system. 

If you want to be more professional and careful about what you’re doing, you want to have a “manifold” which is an 
assembly with three hoses, two gauges, and an assortment of valves.  One hose connects to the low pressure service 
port, another connects to the high pressure service port, and the third connects to the vacuum pump or the freon tank or 
whatever you happen to be fiddling with.  Once connected up, you just open and close valves to service the system.  
Very slick.  And, perhaps more than the home mechanic is interested in paying. 

There is a happy medium solution for the home mechanic.  There is a package offered by Interdynamics, Model No. 
HGT-134A, that contains the short hose and can-tapping valve as in the basic charging kit described above.  It also 
contains a 500 psi pressure gauge.  And it contains an adapter: a quick-disconnect that connects to the high pressure 
service port and presents a low pressure service port to connect your hose to!  That just seems wrong somehow, they 
went to all this trouble to provide different ports so you couldn’t possibly connect the freon can to the wrong port and 
have it explode in your hand, and then they go and make this adapter that allows you to do it anyway!  But as a 
practical matter it’s a cheap way to use one hose to connect that gauge to either port.  Just don’t do anything stupid. 

Note that the pressure gauge, being clearly intended for R-134a use, not only has pressure scales in psi and kg/cm

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 but 

also temperature scales in °F and °C.  Pressure and temperature have a fixed relationship in a closed freon circuit. 

This particular package does not come with a vacuum gauge.  However, the pressure gauge is made with a 1/8” NPT 
connection at the bottom, and it comes in this kit with an adapter screwed onto it that allows the gauge to be connected 
to the R-134a hose fitting.  So if you happen to have a vacuum gauge laying around, you can unscrew this adapter from 
the pressure gauge and screw it onto the vacuum gauge and hook it up. 

 

CHARGING:  Charging is fairly straightforward, and is described in the instructions that come with any kit.  Note that 
the instructions will include putting a large can of ester oil in via the low pressure service port, but if you’ve replaced 
the compressor you should have already added 8.5 ounces of oil in liquid form so you will only be adding a small can at 
most at the port. 

The guidelines on R-134a is to plan on using 85% by weight of the amount of R-12 the system used.  The Jaguar V12 
with the A-6 compressor uses 2.5 lb of R-12, so it should take about 34 oz. of R-134a.  Buy three 12-oz. cans. 

Many people conclude that since it takes fewer ounces of R-134a than it took in R-12, you’re not supposed to fully 
charge the system with R-134a until there are no bubbles in the sight glass.  This is incorrect; no gaseous refrigerant in 
the liquid line is a fundamental requirement of a properly functioning refrigeration circuit regardless of what type of 
refrigerant is used.  The reason we use only 85% as much R-134a is because R-134a is less dense than R-12; the same 
quantity of fluid weighs fewer ounces. 

There are warnings everywhere that the sight glass is not a reliable indicator of proper charge with R-134a.  There are 
two reasons for these warnings.  First, PAG oil will tend to fog over the sight glass under certain conditions, which 
means you won’t be able to see any bubbles whether they are there or not.  Obviously, if you planned on relying on the 
sight glass and neglected to keep track of how many ounces of R-134a you’ve been putting in, you’re screwed.  So 
warnings are in order: keep track of how much R-134a you’re putting in, because the sight glass is not a reliable 
indicator of proper charge.  You didn’t think about it meaning it that way, did you? 

 
 

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Fortunately, the fogging problem apparently doesn’t apply to systems using ester oil.  It may apply to some of the stop-
leak products offered for use with R-134a, though, so it’s still a good idea to keep track of how much refrigerant you’re 
putting in. 

The second reason does apply.  If the condenser is inadequate for use with R-134a and you don’t install an HPCO, you 
will end up with a system that is either undercharged or overheated.  Undercharged is better.  So, while ideally the 
system will have an adequate condenser and run pure liquid in the liquid line, you may be compelled to undercharge the 
system and put up with the (considerable) reductions in performance in order to limit the high side pressures.  A better 
idea would be to install a HPCO switch as described above and fully charge the system -- but if the condenser 
shortcomings are not addressed, it’s going to be cutting off the compressor a lot. 

 

Delanair MkII (up to 1987) 

 

TRAINING MANUAL:  Jaguar, back in the days of British Leyland control, issued a “British Leyland Service 
Division Dealer Training” manual, “Aid # S1002” on the Environmental Control System.  Although it’s described as 
intended for the “Jaguar XJ6, XJ12 Series Two”, the same basic system was used in the pre-1987 XJ-S.  This book is 
long out of print, but if you happen to find a dealer or mechanic with one you definitely want to have a copy made. 

 

SCHEMATIC CORRECTIONS:  This clarification applies to the “Air Conditioning” diagram in at least one early-80’s 
edition of the owner’s handbook as well as Figures 10.125 and 13.94 in Haynes manual 478/49015.  There is a BU wire 
that comes from the left connector on the M1, M2, and High speed relay coils and eventually ends at the low speed 
switch (192D).  Another wire, no color indicated but I’m betting it’s black, comes off the left connector on the Low 
speed relay coil and wraps around the bottom of the entire schematic, clearly the ground for everything.  At the top left 
corner of this diagram, it appears these wires are connected -- but they are not.  A little Liquid Paper is in order to make 
this clear. 

 

HEATER CORE REPLACEMENT:  The heater core (“heater matrix” for you Brits) in the Delanair MkII has integral 
pipes that extend through the firewall, where hoses connect it to the engine cooling system.  To get it out intact requires 
disassembling the entire dashboard and A/C system, including discharging the freon circuit. 

Michael Neal recommends shortcutting the heater core removal to keep from pulling the dash apart.  The instrument 
pod must still be removed, and dropping the steering column down is required.  But total disassembly can be avoided 
by cutting the pipes and installing the new core using short pieces of hose with clamps.  Neal is an official Jaguar 
mechanic and highly recommends this method; there is nothing wrong with using heater hose for such an application, 
and disassembly of the entire system is likely to cause further problems unless done by an experienced Jag mechanic. 

Greg Price sends a detailed checklist:  “To those who have to replace their heater cores and want to cut the pipes rather 
than disembowel their entire interior, the procedure is pretty straightforward with the following caveats: 

1.  You don't have to take the driver's seat out, but it might make a more comfortable working environment. 

2.  The steering column must be removed in order to make room for the heater core to slide out.  The steering 
column is held up under the dash by four bolts.  These bolts have spacers, washers, seating rings and a steel 
piece that holds the nuts.  Before removing the steering column, take out the tach and speedo, then look inside 
with a flashlight to see where all of the little spacers and miscellaneous bits go.  Take notes.  As soon as you 
start to remove the four bolts, all of those bits bail out. 

3.  Take a Polaroid picture of the heater mechanism area before you start taking things out.  If you can't buy or 
steal a Polaroid camera, draw a very detailed map of the area, and pay attention to what goes under or over 
what.   

 
 

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4.  As you remove the screws and such, tape them to a sheet of paper in the order that they were removed.  It 
makes the orderly reassembly that much more orderly. 

5.  Buy the best hose clamps you can find.  Get those swedish jobs that you can torque down with an impact 
wrench.   

6.  Use silicone to seal the hose to the pipes. 

7.  Cover everything.  Twice.  Brass shavings fly everywhere when you cut the pipes (especially if you use a 
pneumatic cutoff tool).  Silicone always ends up everywhere except where you want it. 

8.  Be mindful of the hazard light switch.  It's easily mangled.  I think mine will hold together (I hope). 

9.  Plastic wire ties are great for holding all of the excess wiring and plumbing up out of your way. 

10.  Don't drain your cooling system like the manual says.  Pull off the heater hoses, plug them temporarily, 
then blow the remaining water out of your heater core with compressed air.  Keep your face away from the 
outlet. 

11.  Watch out for the fiber optic line going into the ignition switch cover.  Remove the switch cover and tape 
it up out of the way with the fiber line before you drop the steering column. 

12.  If your cruise control doesn't work, now is a good time to check the steering column wiring and speed set 
switch. 

“The entire procedure took me about 3 and a half  hours (including a short dinner break), which beats the hell out of 
disassembling the dash and console.” 

 

STUB DUCTS:  The stub ducts that the rubber ducts connect to are easily removable; just twist CCW.  This can be 
really handy for getting to some things, such as the 12V terminals on the firewall.  Richard Mansell says, “these can 
also be pulled off to get at the top of the A/C drain tubes.”  To reinstall, just offer them up to the holes and turn around 
until they pop into place, then turn them CW to lock.   

 

BLOWER FANS - INDIVIDUAL SPEEDS NOT WORKING:  The four blower speeds are controlled by four relays 
built into a single unit that is located adjacent to the left side footwell; the footwell register and the small padded cover 
must be removed to get at it.  If one of these four relays quits, one speed of the blowers no longer works, and the A/C 
system just skips over it from the next lower speed to the next higher speed and back.  The result can be a little 
disconcerting, since the bigger change is speed is quite noticeable, and since it may be more change than necessary the 
system can end up cycling back and forth between the two speeds a lot when it would have been happier just staying at 
the middle speed.  Even worse, if it happens to be the “low” speed relay that fails, the A/C compressor can be operated 
without a fan running which is not good on the equipment and may cause the compressor to kick in and out on its own 
thermostat trying to prevent iceup. 

This four-relay assembly appears to be a common failure: this author has had three of the four relays inside it fail, and 
others report similar results. 

I took the box apart and fixed it each time.  The unit is tough to get out of the car, but once out it is a simple matter to 
bend the plastic edges back and pry open; you might even try bending the edges back and prying the base out without 
removing it from the car, since the base will carry all the important parts and you’ll simply leave the plastic housing in 
place.  Be careful; the NW wires connecting to the terminal with the screw (and several of the components inside, if 
you don’t disconnect this wire before opening) are hot at all times unless you have disconnected the battery. 

The coils are designed to be on continuously, so they don’t burn up; the problem always seems to be broken 
connections.  The thin wires from the relay coils break off of the terminals, and soldering them back on makes it work 
as good as new.  However, there is a theory that these long thin wires spanning considerable distances within this 
assembly are the cause of the problems; a vibration in the car, perhaps at a particular speed or engine RPM, may 
resonate these wires like guitar strings and break them off. 

 
 

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So, instead of just reconnecting them, fix the problem.  On each coil, the skinny coil wire comes out of the coil and is 
wrapped a couple of times around a plastic lug on the side of the coil before running off to the terminal.  Solder a larger 
gauge wire to the terminal and route this larger wire to the plastic lug on the relay and wrap it around a couple times, 
then solder the end of the coil wire and the new thicker wire together right next to the lug.  Hence, the thick wire spans 
the distance to the lug, and the thin coil wire is well supported. 

Alternatively, just replace the individual relays that go bad.  Brian Sherwood “Found a portion of the fan control relay 
was inop, no fan on "low".  Removed four wires from bad portion of relay block and plugged into a generic 12-volt 
relay with spade terminals; fan works fine now.  Fan control relay is located in center console, LH side under heater 
unit.” 

The four relays are located at the four corners of the unit.  The “low” relay, at the bottom right corner as you look at it, 
seems to be wired with four wires as Sherwood described.  The other three relays, however, each have two wires going 
to them, plus there are two commons going to the whole set of three.  A large NW wire provides 12V power to all three 
contacts to power the blowers.  A small BU wire provides a common switched ground for all three coils.  The signal to 
the relays comes via BY, BG and BW wires, and the power to the resistor pack and blowers is via larger U, R, and GS 
wires. 

If the low relay fails, you can replace it with a standard automotive relay, such as those sold for driving lights; merely 
remove the four wires from the box and connect the B and NY wires to the coil and the NW and Y wires to the 
contacts, as Sherwood suggests.   

If one of the other three relays fails, you can still replace it with a standard relay.  Connect a wire from the BU wire to 
one side of the coil (without disconnecting the BU wire from the other relays on the board), and simply pull the BY, 
BG or BW wire off the terminal on the faulty component and connect it to the other side of the coil.  Connect a heavy 
wire from the NW wire to one side of the contacts (again leaving it connected to the other circuits), and pull the U, R or 
GS wire from the terminal on the faulty component and connect it to the other side of the contacts. 

Either opening the box and correcting the problems or replacing the relays with individual SP relays would probably 
save a lot of money; generic “driving light relays” will work fine are only a couple bucks each.  It’s likely to cause less 
trouble, too; most of the aftermarket generic relays are quite reliable.  You certainly don’t want to buy a replacement 
four-relay unit from Jaguar -- after all, the original one is causing trouble, and the replacement isn’t likely to be any 
better.  In fact, it might not be a bad idea to simply yank the entire block out of the car and replace it altogether with 
four generic relays at the first sign of trouble. 

Note that British Leyland Service Division Training Manual S1002 on the Environmental Control System shows a 
separate low speed relay and a box containing three relays; since the manual is intended for the XJ6 and XJ12 Series 
Two, this probably describes an early arrangement.  The wiring schematic appears unchanged, however, and the 
replacement of individual speed relays with separate units will work just as well. 

 

BLOWER FAN RESISTOR PACK:  Component #188 on the schematics.  Physically, this unit is mounted in an 
opening high on the left side of the A/C system, above the heater core pipes.  Access to the resistor pack is poor, to put 
it mildly.  If it must be removed, it is suggested that the left side blower assembly be removed first.  It is also suggested 
that a hole be drilled in a piece of structural sheet metal to allow a Pozidriv screwdriver to be used on the upper 
mounting screw. 

The speed of the blower fans is controlled simply by connecting the various resistances in series with the blower 
motors.  These resistor packs are installed in the airstream from the blowers so that the airflow will keep the resistors 
cool.  If the blowers seize or otherwise fail to move air, the result is often a cooked resistor unit due to lack of cooling 
combined with the high current load due to the mechanical problem. 

If one is really cheap or in a hurry, the unit can always be repaired using Nichrome wire from an old toaster or some 
such, or even by twisting severed wires back together.  Do not use solder, as it will melt; all connections must be 
mechanically attached.  Exact resistance values are unimportant, since being off a little will only make the fans run a 
little faster or slower than original.  Note that this unit is so difficult to get to that it would be nice to make real sure it 
doesn’t fail again.