Jaguar XJ-S. Manual - part 131

 
 

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R-134a adapters are supposed to be unremovable once installed, and this is accomplished via some red glue on the 
threads. 

Since the two R-12 ports are the same on the XJ-S, I will explain clearly which is which.  The port on the line from the 
fuel cooler to the compressor is the low pressure port and therefore should have the smaller diameter R-134a adapter 
with a blue cap screwed onto it.  The port on the muffler on the line going to the condenser in front of the radiator is the 
high pressure port and should get the fatter adapter with a red cap screwed onto it. 

 

LOW PRESSURE PORT ADAPTER:  The R-12 ports on the car each have a Schrader valve (tire valve) that seals the 
freon inside unless the pin in the center is depressed.  An R-134a low pressure port is a relatively small diameter fitting, 
smaller OD than the R-12 threaded fitting, so the adapter must hold the R-134a fitting out off the end of it.  Of course, 
that’d make pushing the pin within the R-12 fitting down inside difficult. 

The solution used on the Interdynamics low pressure port adapter is to install a floating pin in the center of the adapter.  
If you hold the low pressure port adapter up to your ear and shake it, you can hear it rattling around in there.  There are 
no springs or seals involved.  When this adapter is installed, pressing on the end of this floating pin will depress the pin 
in the center of the Schrader valve in the R-12 fitting below. 

As mentioned above: it’s a good idea to replace the Schrader valves whenever the system is discharged, just as you 
would replace the O-rings whenever working on an assembly.  Of course, with that Interdynamics port adapter screwed 
down over it with Loctite in the threads, that looks like it may present a challenge -- so by all means replace that 
Schrader valve before installing the service port adapter! 

If you’re already past that point and need to replace that Schrader valve, you could of course just force the adapter 
loose, replace the valve, and reinstall the adapter -- or install a new adapter if you messed that one up getting it off.  
However, it is actually possible to replace the Schrader valve through the adapter.  The pin assembly within the 
Interdynamics adapter can be unscrewed and removed, leaving an opening large enough to get a Schrader valve 
through.  It’s gonna be fiddly, though. 

Look at the low pressure service port on your XJ-S V12 -- the port on the tube connecting to the left rear side of the 
compressor, coming from the fuel cooler.  On the author’s ‘83 it points upward, although reportedly it may have 
different orientations on later cars.  As discussed above, the R-134a low pressure service port adapter sticks off the end 
of the R-12 port -- and then there’s a cap that screws onto that.  Altogether, the adapter and cap sticks up perhaps 3/4” 
farther than the R-12 port and cap did.  If your service port points upward, you might complete the job and close the 
hood on this project only to be rewarded with a dent sticking up in the middle of your hood!  And just because it clears 
when the hood is closed doesn’t mean you’re out of the woods, either; when the engine twists on its rubber mounts -- 
especially if the left mount fails -- the engine could jam that fitting into the hood when you trounce on the throttle.  All 
in all, there is a good argument here for ordering new R-134a hose assemblies, or at least this one, since that fitting will 
be shorter. 

Alternatively, of course, you could modify that tube while rebuilding the hoses, either replacing the R-12 port with a 
brazed-on short R-134a port or at least relocating the R-12 port somewhere more convenient.  Or just abandon that port 
in place and add a new R-134a port somewhere else in this line.  Or, considering how common the GM A-6 compressor 
is, find a low pressure line from a different type car -- possibly in a junkyard -- and adapt it to the XJ-S. 

You might be tempted to try rotating the hose assembly around the connection at the back of the compressor just a bit to 
lean this fitting over on the side.  The problem there is that you will be leaning the service port towards the 1B fuel 
injector hose.  Keep in mind that the quick-disconnect fitting that connects to an R-134a low pressure service port is 
fatter than the one that fits an R-12 port, so you need more clearance around that port, not less.  Also note that the R-
134a quick-disconnects come in brass or plastic versions, and the plastic versions are even fatter than the brass.  You 
may find that you need to roll that hose the other way to pull the service port farther away from the 1B fuel injector 
hose! 

Since the Schrader valve remains in place within the R-12 port, here’s the easiest solution:  Carefully pry the O-ring out 
of the low pressure port adapter and unscrew the floating pin device.  Then use a pistol cleaning brush of an appropriate 
size (about .41 caliber) to scrub all the red stuff out of the threads.  Put the O-ring and floating pin device back in.  Use 

 
 

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some anti-seize compound for good measure, but apply it only to the male threads on the R-12 port to make sure it can’t 
get inside the system.  Service the system, then remove the adapter and put the R-12 cap back on.  Store the adapter in 
the glove compartment.  Apply a label explaining clearly that the adapter needs to be removed before closing the hood. 

Interdynamics is not the only company making port adapters.  There are adapters made by other companies (sometimes 
of brass or steel rather than aluminum) that, rather than using that cute floating pin idea, have a Schrader valve built in.  
You must remove the Schrader valve in the R-12 port prior to installing the adapter.  Hence that idea of removing the 
adapter when closing the hood will not work.  For adapting the XJ-S, it might be a good idea to insist upon the 
Interdynamics adapter with the floating pin; listen for the rattle when you shake it. 

 

HIGH PRESSURE PORT ADAPTERS:  There are at least two types of high pressure port adapters that will work on 
the XJ-S.  The first type looks similar to the low pressure port adapter described above except larger -- but it works 
completely differently.  While the Interdynamics low pressure port adapter contains a floating pin, their high pressure 
port adapter contains an actual Schrader valve.  Shaking reveals no rattle, since a spring holds the valve firmly seated.  
With this type, you are supposed to remove the Schrader valve from the R-12 port before installing the adapter. 

Make sure the Schrader valve inside the service port adapter is securely tightened down (ask me how I know!).  You 
can try to blow through it before installing it to check for leaks.  Using one of those tire valve caps with the Schrader 
valve tool on the end won’t work here, the Schrader valve is recessed too far down inside the R-134a service port.  So, 
you will either need to make a suitable tool from some small tubing, or you’ll need to buy a tool.  If you’re lucky, you 
may have a pair of hemostats that will work well enough. 

The fitting for the R-134a high pressure port is larger than the low pressure port, large enough to fit around the threaded 
R-12 fitting rather than out in front of it.  So, eventually somebody figured out that you could skip building a tall high 
pressure port adapter with the Schrader valve inside and instead just provide a short adapter that screws around the R-
12 port and uses the original Schrader valve in its original location.  Very slick, actually.  This author actually found 
kits on the shelf that showed the first type of adapter on the box and in the instructions but contained the second type of 
adapter and a separate slip of paper indicating the substitution. 

The high pressure service port on the XJ-S is located where either type of adapter should fit without hitting the hood.  If 
you are concerned, just make sure to get the second type which is no taller than the R-12 port, just fatter. 

 

OTHER NON-STANDARD STANDARDS:  Besides the test ports, there are two other connections on R-134a 
equipment that differs from R-12.  The connection on top of a freon can is different, having a threaded attachment.  
And the connection between the other end of the test hose and the test equipment (valve or whatever) has a unique 
threaded fitting.  These differing standards are intended to help A/C shops avoid mixing up stuff used with different 
freons. 

They can be a real PITA for the home mechanic, though.  Connecting R-134a-compliant hose to your vacuum pump 
may present a challenge.  There are adapters made, but they can be difficult to find.  The easiest solution may be to cut 
one end off an R-134a hose and attach a suitable fitting using an EFI clamp. 

 

HOSES:  The concern here is that the molecules of R-134a are smaller than molecules of R-12 and may actually leak 
right through the materials used to make R-12 hoses.  So, even without being able to positively identify a leak, the 
system seems to bleed down over time.  The solution is the “barrier hose”, a type of hose that won’t leak R-134a and is 
usable with either R-134a or R-12. 

Bob Staff presents a dissenting view:  “Barrier hoses are not required for a conversion to R-134a.  Experience has 
shown that the systems operate fine without them.  The age of your car may lead you to consider hose replacement.”  
Some suggest that while in theory the non-barrier hoses will leak, in practice the oil in the system tends to coat the inner 
walls of the hoses and seals them.  Others claim that the system will leak, but will only leak a few ounces per year, so 
it’s cheaper to just top it up every now and then than to replace the hoses. 

 
 

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If you buy a hose today -- even one with R-12 service ports on it -- this is a non-issue; all modern automotive A/C 
hoses are “barrier” type.  And at some point in time that probably became the case with the OEM R-12 hoses on a 
Jaguar XJ-S.  However, there was a time before that when the XJ-S came with non-barrier hoses. 

Unfortunately, barrier hose cannot be installed using the threaded hose connections found on the non-barrier hoses on 
the author’s ’83.  Fortunately, as long as the tubes are steel, any industrial hose shop can come to the rescue.  They 
simply saw off that hokey threaded fitting and braze on a barb and crimp the barrier hose to that.  It’s not even 
particularly expensive.  As an example, I had the two low pressure hoses rebuilt, and the only fitting they had to cut and 
braze was the one that connects to the compressor with the service port on it; the other three fittings were replaced with 
brand new aluminum fittings.  The total for two new hoses, three new fittings, one braze job, and four crimps came to 
less than $50. 

I can’t prove it, but I highly suspect that if your XJ-S has aluminum tubes, it also already has crimped connections and 
barrier hoses. 

See page 507 for general guidelines on A/C hose rebuilding. 

You can simply purchase new hose assemblies from Jaguar with either R-12 or R-134a service ports on them -- if 
you’re made of money.  Or you can purchase them from John’s Cars (page 715), reportedly much cheaper.  Remember, 
it doesn’t matter which type service ports it has, a new hose will be the barrier type. 

 

OIL:  There are three types of oils to discuss here.  The oil used with R-12 is called mineral oil.  There are two types of 
oil used with R-134a called ester oil and PAG oil.  There actually appear to be two versions of that last one, PAG 1 and 
PAG 2. 

Mineral oil is worthless in an R-134a system.  The oil within a freon system is dragged around the circuit by the 
refrigerant with the sole purpose of lubricating the compressor.  In order to get to the compressor, it must mix properly 
with the refrigerant and travel with it.  Mineral oil will mix with R-12 and travel around the circuit, but it won’t mix 
with R-134a; it just settles to the bottom of the condenser or whereever and the compressor seizes up.  So, you must use 
either PAG oil or ester oil in a system with R-134a. 

If you leave the old mineral oil in there settled to the bottom and then use ester oil with the R-134a, you may be in 
trouble.  Mineral oil won’t mix with R-134a, but it does mix with ester oil.  The result is that the ester oil ends up all 
dissolved in the old mineral oil, and they both settle to the bottom -- and your compressor runs unlubricated.  Just how 
much trouble you end up in apparently depends on exactly how much mineral oil got left in the system.  If you think 
you’ll be leaving a significant amount in there, you should plan to use PAG oil -- which doesn’t mix with mineral oil 
and therefore will lubricate the compressor no matter what. 

The recommendations of “experts” fall into two camps here.  The major automakers, laying out shop procedures for the 
mechanics in their dealerships to conduct R-134a retrofits, recommend that the system should not be flushed and PAG 
oil should be used with the R-134a.  They claim, as in the excerpt from Jaguar above, that this is because it’s not 
possible to flush all the mineral oil out.  Skeptics believe they actually have other reasons.  For one thing, not having to 
even try to flush saves the shop time and effort.  But perhaps more importantly, not having to deal with the solvents 
necessary to flush an R-12 circuit keeps the EPA, the fire department, and the A/C component manufacturers off their 
backs.  In years past, substances used to flush R-12 circuits have included R-12, mineral spirits, and a host of other 
substances, all of which were trouble one way or another -- and some of which were arguably of limited effectiveness 
in getting the old mineral oil and contaminants out. 

Everybody except the major automakers suggests that you flush the system and then use ester oil with the R-134a.  For 
one thing, suitable solvents for flushing are now commonly available -- although they’re not cheap.  You can buy 
flushing solution in any auto parts store for around $15/quart. 

For another thing, the mineral oil takes up space within the system; the less mineral oil that’s in there, the more R-134a 
you’ll be able to put in.  Note that for some reason R-12 systems often seem to have a lot more mineral oil in them than 
specified.  Apparently each shop that works on the system tends to put more oil back in than they took out, probably 

 
 

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just to be on the safe side.  The massive accumulations of oil over the years of service detract from the performance of 
the system -- and adding in the ester oil on top of it may result in very poor performance indeed. 

There are also theories that the mineral oil, when not being suspended by R-12 any more, tends to coat the inside 
surfaces of the condenser and evaporator, impeding heat transfer and reducing the effectiveness of the system.  When 
somebody complains that converting to R-134a resulted in less cooling capacity than R-12, it’s more likely they’re 
experiencing these sorts of problem than seeing the true difference in the refrigerants. 

Note that you’re not supposed to flush through either the compressor or the dryer.  Plan accordingly. 

If you intend to continue to use non-barrier hoses with the R-134a, it’s also not recommended that you flush the hoses.  
The solvents will remove the mineral oil from the inside surface, increasing the likelihood that the hoses will leak R-
134a. 

This system will require about 10-12 ounces of oil.  Ester oil comes in pressurized cans containing oil plus some R-
134a; the 11-ounce can provides 8.5 ounces of oil, and the 4-ounce can provides 2 ounces of oil.  If all you’re doing is 
converting a working system, one can of each size would be a good oil charge. 

If you’re replacing the compressor, it is generally recommended that you put some liquid oil into it prior to installation. 
 Ester oil is also available as an 8.5-ounce can of liquid for such purposes. 

If the compressor has too much oil in it while it’s being installed, some of it may leak out when the caps are removed 
from the suction and pressure ports to connect the hoses.  Aside from being messy, having an unknown amount of oil 
leak out means that you won’t know how much oil remains inside.  James Teston suggests “Depending on what you are 
taking apart, you may be able to connect the high and low pressure hoses to the compressor end before you install the 
compressor.”  He suggests you can tighten the attachment bolt enough to effect a seal but loose enough that you can 
reposition the hoses the way you want them after the compressor is in place. 

This author recommends the following procedure for adding ester oil to a dry compressor being installed in a flushed 
system.   First, with the compressor on the bench with the nose downward and the ports upward, put some liquid oil in 
the suction port -- but no more than three or four ounces.  You may need to turn the hub at the front a bit to get even 
that much oil to go in, but don’t turn it more than one full turn because it’ll start pumping the oil out the pressure port.  
Reapply the caps or install the hoses and cap the other ends of the hoses; ester oil will absorb moisture from the air, and 
you want to minimize that happening.  Ideally, let the compress sit nose-down for a while to allow the oil to seep down 
towards the front seal.  Install the compressor.  Then with the suction line disconnected from the fuel cooler (disconnect 
it if necessary), hold that end of the hose upward and pour the rest of the oil from the 8.5-ounce can directly into the 
end.  As it flows down towards the compressor, turn the hub of the compressor slowly by hand to help draw it into the 
works.  After the system is buttoned up and evacuated, add another 2 ounces of oil while charging by connecting a 4-
ounce can to the low pressure service port. 

 

O-RINGS:  Jonathan Sterrett says, “There is no incompatibility between the refrigerant types and the O-rings in 
question, but rather between the early R-134a lubricants (PAG) and O-rings used in R-12 systems.  The new ester oils 
are compatible with the O-rings from R-12 systems.” 

The O-rings used in an R-12 system will not dissolve when used with R-134a or PAG oil.  That’s not the concern; the 
concern is with the size.  If you take two identical O-rings and use one in R-12 and the other in R-134a, the one in R-12 
will end up a bit larger than the one in the R-134a. 

Imagine the O-rings in your system are in good shape, rubbery and pliable, and are properly compressed between 
surfaces in their respective installations.  Then the R-12 is replaced with R-134a and the rubber shrinks a bit 
accordingly.  Will this cause a leak?  Probably not.  The compression of O-rings is generally far more than the 
shrinkage caused by the refrigerant change.  Hence, the kits don’t mention having to replace O-rings. 

Now, imagine the O-rings in your system are old and tired.  They’ve been in there for a few years being subjected to 
heat soak every time you park the car in the sun on a hot summer day.  If you could pull them out and hold them in your 
hand, they wouldn’t have a round cross-section; they’ve taken on the distorted shape they got from being compressed.