Jaguar XJ-S. Manual - part 132

 
 

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They’re still not leaking, though.  Now, when you replace the R-12 with R-134a and they shrink a bit, are they gonna 
leak?  You betcha! 

Before you go worrying a great deal about this issue, note that all of the O-rings in the XJ-S are relatively easy to get to 
and replace.  Well, except perhaps those at the expansion valve -- but you may be replacing the expansion valve as well 
after you read about it below. 

Yes, there are special O-rings made for R-134a conversions.  They are typically blue or green -- but the color is merely 
a light dusting of chalk, you can rub it off and the O-ring itself is black underneath.  The color indicates that this O-ring 
is a hair fatter than the standard O-ring, making it compress properly in grooves sized for standard O-rings exposed to 
R-12.  The dust also helps you get the parts together, which may otherwise be a little difficult with O-rings that are 
fatter than the assembly was intended to fit. 

Although the colored O-rings are generally easy to find, if you prefer you can use standard black neoprene O-rings.  
Installed new, they will work fine.  Apply a bit of compressor oil when installing to make them slide together easily. 

You may be surprised at how few O-rings you need to buy.  When this author rebuilt his system, the new compressor 
and the new expansion valve came with new O-rings.  The shop that rebuilt all three hoses returned them with new O-
rings for the standard fitting ends.  The only component that didn’t come with new O-rings was the dryer, presumably 
because it has female ends rather than male ends. 

 

COMPRESSOR:  There are two concerns in the compressor: O-rings and the shaft seal.  The O-rings are discussed 
above.  You’re not likely going to take the compressor apart to replace O-rings, but as suggested before it’s not likely 
you’re converting to R-134a for nothing -- you have probably decided to convert in the midst of a compressor 
replacement!  If so, don’t worry about the O-rings; any rebuilt compressor will have been assembled with suitable O-
rings. 

Joe Bialy says, “Jag sez that only Sanden units need to have their shaft seal replaced for R-134a retrofits.  The Harrison 
does not require any modification at all.” 

 

EXPANSION VALVE:  The general discussion on the expansion valve is on page 506.  The expansion valve is a 
throttling valve that responds to pressure.  As discussed in an earlier section, pressure within a closed freon circuit is a 
function of temperature.  The expansion valve is trying to hold the evaporator at a pressure corresponding to a 
temperature in the 30’s F. 

Now you go and replace the R-12 with R-134a.  The pressure in the system is still a function of temperature, but it’s 
now a different function of temperature.  The expansion valve is still trying to hold the same pressure, but that pressure 
no longer corresponds to a temperature in the high 30’s F.  It apparently corresponds to a temperature in the 50’s, if the 
reports from people who have done this conversion are any indication. 

Once again, the switch to R-134a is blamed for a loss of performance -- but it’s not the R-134a’s fault, the wrong 
expansion valve is in there!  Regardless of “capacity”, the system should provide air in the upper 30’s F when lightly 
loaded.  If the wrong expansion valve is used, it’ll never get colder than 50’s F regardless of load.  This isn’t a capacity 
issue, it’s a control issue -- the expansion valve is not controlling the refrigerant flow properly. 

Ed Sowell reports that the expansion valve he got for his conversion was clearly labelled as being for R-134a.  It’s not 
likely anyone would bother with such marking if the expansion valves weren’t different for R-12 and R-134a. 

Again, the kits don’t mention replacing the expansion valve.  Perhaps they consider 50°F air cool enough.  It’s not 
really, though, since it won’t dehumidify as well and it will require more fan speed to achieve comparable cooling.  If 
you want this system to work right, replace the expansion valve. 

Having to replace the expansion valve might, at first blush, seem a powerful argument for going with Freeze-12 or one 
of the other refrigerants that claim to be a functional equivalent of R-12 and therefore don’t require an expansion valve 
change.  Not only is the R-134a expansion valve perhaps $35, it’s also a serious PITA to get to in the XJ-S.  There’s 
one more factor to consider, though: if you’re replacing the compressor and the rebuilt compressor you get has any sort 

 
 

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of warranty on it, that warranty always requires that the dryer and the expansion valve be replaced along with the 
compressor.  Since the rebuilt compressors seem to vary greatly in quality and reliability, that warranty is important.  
You probably want to replace the expansion valve.  And be sure to keep the receipts for both the expansion valve and 
the dryer, especially if you buy them somewhere other than where you get the compressor. 

 

DRYER:  The general discussion on the dryer is on page 506.  When converting to R-134a, the desiccant inside the 
dryer must be compatible with R-134a.  Apparently all modern dryers are compatible with either R-12 or R-134a, but 
some original dryers may not be compatible with R-134a.  At this point, if there’s still a dryer in there that’s old enough 
it might not be compatible with R-134a, replace it. 

Again, the kit doesn’t mention replacing the dryer.  They are describing replacing the refrigerant in a perfectly working 
system, one that hasn’t sprung a leak.  They’re apparently also presuming the system is new enough that the dryer is 
compatible with both refrigerants.  If your system has been opened or sprung a leak and lost all the refrigerant, you 
probably should replace the dryer anyway. 

 

CONDENSER:  Let’s say that in order to transfer enough heat to keep your sorry butt cool, the condenser in your XJ-S 
must operate at 150°F.  With R-12 in the circuit, this would mean that the compressor must produce 235 psi in the high 
pressure line.  Now, you convert to R-134a.  To attain the same 150°F in the condenser in order to transfer the same 
amount of heat, the compressor must now produce 263 psi in the high pressure line. 

There are two things you can do about this.  One is to upgrade the condenser somehow so that it moves the same 
amount of heat at a lower temperature than before, so that the pressures are in line with what they were before.  In this 
particular example, getting the temperature of the condenser down to 140°F would do it. 

The other thing you can do is -- nothing.  Just let the system operate at the higher pressures.  Obviously, there are 
information sources that won’t suggest you do this because they don’t want to be liable if you blow hoses or destroy a 
compressor.  And there are other information sources that note that operating at higher pressures is not usually that big 
a deal and perhaps not worth the hassles to address. 

Before you latch onto the latter choice, allow me to remind you that excessive high side pressures are already a known 
concern with the XJ-S.  You should be so lucky as to be running at 235 psi with R-12; it’s more likely well over 300 
already.  You can review this problem on page 514.  When you consider that the car may already be stressing the 
compressor and lines to the breaking point, switching to R-134a is just begging for trouble. 

If you have the stock belt-driven fan and everything else in the airflow situation is OEM, I would recommend that you 
do not switch to R-134a without addressing the condenser situation.  Sure, if your fan clutch is in perfect condition, the 
idle isn’t set too low, the foam surrounding the radiator and condenser is intact, there are no leaves or debris in there 
plugging up the airflow path, etc., etc., you might be able to get away with it.  You’re still likely to have a system that 
performs poorly, though.  

There are two ways to increase the condenser capacity so that it can operate at lower temperatures.  The first is to 
replace the condenser itself with a bigger one -- commonly described as a “parallel flow” or “multipath” condenser.  
There are many aftermarket businesses that offer such condensers.  According to the documentation quoted above, 
Jaguar went with a “parallel flow extended height” condenser when they introduced an R-134a system in the XJ-S in 
1994; perhaps this unit can be adapted to earlier models. 

The other way is to increase the airflow through the condenser.  The cheap and easy way would be to add a “pusher” 
electric fan on the front of the condenser blowing through it.  You can simply wire a relay to operate the fan whenever 
the compressor is engaged.  Or, you can wire it to come on whenever the small OEM electric fan comes on, so it can do 
double duty and help keep the engine cool as well. 

Of course, you could go ahead and replace the belt-driven fan with a powerful electric fan or any of the other various 
suggestions along these lines presented beginning on page 219. 

 
 

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If you have one of the later cars that doesn’t bring on the small OEM electric fan when the compressor comes on, by all 
means revise that wiring so the fan comes on.  This arguably should be done regardless, but with the conversion to R-
134a it becomes doubly important. 

Chuck Sparks suggests that, while you have the system torn apart anyway, take the condenser out and give it a good 
scrubbing to get all the road grime off the outside.  This will make it transfer heat better.  Of course, one could argue 
that it would merely give you false confidence in your system, since obviously it’ll have more road grime on it 
sometime after you get this system together and running. 

 

HIGH PRESSURE CUT OUT SWITCH:  If you read that last section on the condenser, perhaps you understand why 
some suggest installing a High Pressure Cut Out (HPCO) switch that disengages the compressor if the pressure exceeds 
a certain value.  If the condenser capacity problem isn’t addressed, such a switch will likely result in the compressor 
cycling on and off.  Basically, the condenser will get hotter and hotter until the switch shuts the compressor off, then the 
condenser can cool off until the compressor comes back on.  This will provide cooling, just at a reduced capacity.  It 
also may cause premature failure of the compressor clutch, what with all that cycling. 

Of course, you really should address the condenser issues as described above.  It won’t hurt to install the HPCO switch 
anyway, but if you do the condenser job right it’ll never come into play. 

If you’re not confident of your condenser/airflow situation, by all means install a HPCO switch.  If the pressure exceeds 
430 psi, the pressure relief valve on the back of the compressor will piss away your freon until the pressure drops to 
safe values.  After that your system will remain undercharged and never cool as it should, even when there is adequate 
airflow through the condenser!  With the high pressure switch, the compressor can be shut off to limit pressure without 
losing any refrigerant which leaves it properly charged so it can cool properly when pressure isn’t an issue -- such as 
when the car is moving at highway speeds and there is gobs of air flowing through the condenser.  With any luck at all, 
the high pressure switch will only come into play when the car is idling at a stoplight in hot weather. 

“Muxika” describes the HPCO switch:  “...a cut off switch connected in series with the A/C clutch set at 350 psi. 
(GM/AC Delco part # 15-5514).”  The GM part number is 15981985.  A search of the www turned up switches that cut 
out anywhere from 325 psi to 410 psi.  As reference:  Ideally the high pressure side should operate around 250 psi (17.5 
kg/cm², 145°F, 63°C), and anything over 325 psi (22.8 kg/cm², 165°F, 74°C) should be considered overheating. 

Any suitable HPCO switch has either internal damping or a wide dead band or both to make sure the compressor 
doesn’t cycle on and off too quickly. 

White Industries (

http://whiteac.com

) also offers such a switch, part number 03245-SP.  You can also get one that’s 

made by 

FJC 
Post Office Box 499, Mt. Mourne, NC  28123-0499 
101 Commercial Drive 
Mooresville, NC  28115 
704-664-3587    Fax: 704-664-5522 

http://www.fjcinc.com/

 

Their HPCO switch part number is 3245.  Hmmm.  Seems related to that White Industries number. 

As long as you’re plumbing in an HPCO switch, you can plumb in a switch that does more.  You can purchase a 
“binary safety switch” which not only shuts off the compressor if the pressure is too high but also shuts it off if the 
pressure is too low -- which would mean the freon has all leaked out.  Later XJ-S’s come with a low pressure switch 
already built into the back of the compressor, but if you have an earlier car with a 3-terminal fuse you might want to 
consider a binary safety switch and abandon that 3-terminal fuse idea -- especially if your replacement compressor 
doesn’t have the correct type port to fit the temperature switch that operates the 3-terminal fuse. 

You can also opt for a “trinary switch”.  Besides the two functions of the binary safety switch, the trinary switch will 
also bring on an electric fan on when the pressure rises above 220 psi.  That means it only runs the fan when truly 
needed rather than whenever the compressor is on. 

 
 

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There are dozens of places that offer binary and trinary switches, often specifically intended for particular cars -- none 
of which ever include Jaguars.  For our purposes, you can use a generic.  You can get one from 

Hot Rod Air, Inc. 
9330 Corporate Drive, Suite 308 
Selma, TX 78154 
Orders: 1-877-693-3200 
Tech: (210) 651-0040 

 

Fax: (210) 651-0070 

http://www.hotrodair.com/

 

E-Mail: sales@hotrodair.com 

Once you pick a switch, you must connect it into the high pressure line.  There are at least four ways to do this.  One 
option is to purchase a “saddle clamp” that clamps onto the outside of a tube and then a pin is screwed down to 
puncture the tube underneath.  GM dealers have such a saddle clamp, part number 15985307. 

Another option is to purchase a tee that is fitted to the high pressure service port and provides a switch port and a new 
service port.  Conveniently, these are available that screw onto the R-12 port and provide an R-134a port, so it replaces 
the high pressure port adapter.  Make sure to get one that fits the pre-1976 R-12 high pressure port which is a 1/4” flare 
fitting.  White Industries offers a suitable tee, part number 02638-SP.  FJC also offers the correct tee, part number 2638. 
 Hmmm, they seem related again. 

As an aside here, several companies offer a selection of “service port extension hoses”.  These are hoses about a foot 
long that you screw onto a service port and leave in place permanently, and use the other end of the hose as your 
service port.  The intent is to deal with service ports that the automaker chose to put in totally inaccessible locations.  
There are no such access problems on the XJ-S, the service ports are right up top -- but you might opt to use one of 
those service port extension hoses to locate your service port adapter tee and HPCO switch somewhere where the hood 
won’t slam on it! 

Another method for connecting your HPCO switch is with a tee that is installed at a hose connection.  On the XJ-S, this 
would have to be installed at the right front corner of the engine compartment where the high pressure hose connects to 
the line to the condenser.  The hose connects to the tee, the tee screws onto the condenser line.  It effectively makes the 
hose a little longer, but that shouldn’t hurt anything.  Hot Rod Air offers such a tee. 

A fourth method is a tee that is spliced directly into the high pressure hose.  It’ll require a crimping tool to install, but if 
you have a crimping tool it may be the cheapest option. 

Pressure is a function of temperature in a refrigerant circuit, so in lieu of a pressure switch you could install a 
temperature switch.  This might be easier as an add-on, since a temperature sensor can be strapped onto the outside of a 
tube rather than having to be connected into the line itself. 

 

COMPRESSOR CYCLING SWITCH:  Some automobiles have a “cycling switch” that turns the compressor off when 
the low side pressure gets too low.  Pressure corresponds to temperature in a closed freon circuit, so what it’s really 
doing is preventing the evaporator from getting too cold and possibly icing up.  Since switching from R-12 to R-134a 
changes the pressure/temperature relationship, you need to adjust or replace this switch so that it cycles the compressor 
off at the correct temperature. 

The XJ-S doesn’t have a compressor cycling switch.  Instead, it uses a Ranco thermostat that directly measures the 
temperature of the air coming off the evaporator and cycles off the compressor if this air gets too cold.  So there is no 
need to worry about this when changing refrigerants. 

 

CHARGING EQUIPMENT:  It would make sense to describe charging equipment in the general section on the A/C 
rather than in this section on R-134a, but it’s difficult to find R-12 stuff any more and you need a license to buy it 
anyway.  The R-134a equipment is readily available to anyone in any auto parts store.