R12 to 134A Conversion

What should be a reasonable cost to convert the A/C from R12 to 134A? Have reinstalled the old receiver drier in order for system to be purged clean. Have new receiver drier to provide the shop that does the work. Any suggestions from experienced converters welcomed.

What should be a reasonable cost to convert the A/C from R12 to 134A?
Have reinstalled the old receiver drier in order for system to be
purged clean. Have new receiver drier to provide the shop that does
the work. Any suggestions from experienced converters welcomed.

The difference between doing that conversion yourself and paying someone
to do it is vast. At its simplest, it’s simply a matter of recovering the old R-12,
replacing the drier, evacuating, and charging with R-134a. However, there
are risks with that simple version, and shops will sometimes go ahead and
figure in contingencies to cover their asses – which can make the quotes
quite expensive. Here’s a few:

  1. You probably should replace the expansion valve. The system will run
    with the R-12 expansion valve, but it won’t cool as well as it will with a proper
    R-134a expansion valve.

  2. O-rings swell a bit when exposed to R-12, and the grooves they fit into
    are sized accordingly. O-rings swell LESS when exposed to R-134a, and
    over time after a conversion they will shrink back a bit. If they are nice and
    supple, this is no problem, but if they are old and stiff they can cause leaks.
    For years you could buy O-rings that were just a tad thicker than the
    standard 1/8" to replace all the O-rings in the system with; they are typically
    coated with green chalk dust or the like but are black neoprene when you
    wipe the chalk dust off. Special O-rings are wholly unnecessary, though; at
    the worst you’d need to replace the old O-rings with new standard O-rings.
    Obviously, it’d be smart to replace all you can while the system is

  3. The hoses used for R-12 can leak R-134a right through the rubber
    because the molecules are smaller. So, a switch to R-134a sometimes
    includes new “barrier” hoses. Unnecessary, though, because the lubricant
    that cycles through the system coats the inside of the hoses and prevents
    leaks. Still, if your hoses are old anyway…

  4. The biggie: R-134a requires the condenser to work harder. You can use
    the OEM condenser, but the air passages through the radiator fins MUST be
    clear, the fans MUST be up to snuff, and air leak paths around the
    condenser MUST be plugged. Anything less than ideal airflow in an XJ-S will
    result in condenser overheating, which in turn yields skyrocketing refrigerant
    pressures that end up getting vented to atmosphere. You can opt to install
    an aftermarket double-pass condenser, which is great, but my choice was to
    replace the belt-driven fan with an electric fan to ensure excellent airflow at
    idle. You also must fill the 1/2" gap between the top of the oil cooler and the
    bottom of the condenser, which I filled with a strip of weatherstripping.

  5. Be aware that you’ll probably need to “top off” the refrigerant charge after
    you get the car back from the shop. The drier you have should have a sight
    glass; if it doesn’t, take it back and get one that does. When fully charged
    and running continuously, there should be no bubbles in that sight glass. If
    there are, you need to add refrigerant. Too many of these shops add
    refrigerant by weight rather than by using the sight glass, and the weight
    specs are always too light and leave the system undercharged. Some shops
    will see the pressures going high (see above) and reduce the charge; these
    guys should be fired for incompetence. And, of course, they may have
    charged the system properly but the pressure relief valve on the compressor
    pissed some of your charge away, in which case you need to fix the airflow
    problem FIRST and then top off the refrigerant charge.

– Kirbert

To do it correctly, you need to flush the system, replace the hoses (R134 requires barrier hoses and will slowly leak otherwise), replace the o-rings, dryer and expansion valve.

Depending on the climate, you may want to source a parallel flow condenser which has more efficient cooling and allow you to add more volume.

I’m not sure how well the sight glass works with R134. It’s a higher gas by volume and really be charged by weight, at around 80% of the R12 volume.

I prefer charging by pressure as pressure is pressure.

I’m not sure how well the sight glass works with R134.

There are two different types of lubricant used in R-134a systems; one is
generally used in new systems while the other is preferred for retrofitting
R-12 systems. ONE of those lubricants has a tendency to cloud up a sight
glass, rendering it difficult to see bubbles whether they are there or not. As a
result, techs are given instructions on charging without relying upon the sight
glass, and in some cases the sight glass is even omitted. When I converted
my '83, though, I had no difficulty seeing bubbles in the sight glass.

If you CAN see bubbles through the sight glass, then the sight glass should
be your final arbiter on whether the system is fully charged. If you can see
bubbles when it’s running under steady conditions, it’s low on refrigerant.
That’s a simple fact of a refrigerant circuit, and is not contingent on what type
of refrigerant is used. Under normal operating conditions, the liquid line
should have only liquid in it, no vapor. Period.

It’s a higher
gas by volume and really be charged by weight, at around 80% of the
R12 volume.

The density of R-134a is lower than R-12, which is something that must be
taken into account when charging by weight. It’s not an excuse to
undercharge the system, though. It merely means that the same volume of
refrigerant will weigh less.

I prefer charging by pressure as pressure is pressure.

That’d be good if you could be confident that the airflow through the
condenser is sufficient. Problem is, it often is anything but in this car. And
when the pressures are high and have not stabilized as they should when
charging, simply reaching a particular number on the gauge and shutting
down the charge is not the way to a properly operating air conditioner.

Charge until there are no bubbles in the sight glass. If the pressures are too
high, then you need to address the condenser; it is overheating.

– Kirbert

I’m running propane/ butane. Works really good, need less fluid

Bigger molecules too so less leaks or need to replace hoses!

Having done this three times to my old Jags, you should do all of the suggested items.… modern condenser really makes a big difference… new hoses are “required” in my opinion as well as the new proper R 134 O rings.Changing out the expansion valve now is also a great idea… I had to do it after my last conversion…now get 39F at the side vents in my S1…

What about the oil? Does it need flushed, can the same type be used and how much. Also if flushing is required what kind of solvent should be used?
I have hesitated changing my XJ6 to R134a but must address this as hot summers, black cars and wives do not mix with out AC.
Good post guys!
Ken J

There are a number of ways to to R134a conversions, from minimalist to 1st class and many variations in between. Whether you hire out or DIY, understand what is being done and why. I cannot specifically address the XJS, but I have done several of these incl. my 85VDP.

The minimalist approach involves just changing oil and refrigerant (AC pros call these “death kits”). Basically, it’s a gamble. If all the components are in great condition and the procedure is done carefully, it can work. If everything is not just right, it can fail spectacularly immediately (called “black death”) or operate marginally for a short period of time. Furthermore, the Delphi A6 compressor is/was/and will always be a lousy compressor. If it leaks, finding a QUALITY rebuild is virtually impossible. IMHO you are better spending your money on liquor, women, and gambling; it’s more fun.

The 1st class approach is involved, essentially replacing everything in the engine compartment.

  • Replace the A6 with a much superior Sanden-style compressor. Fabricate a mount.
  • Custom R134a barrier hoses
  • Replace expansion valve and drier
  • If the condenser is tube&fin, replace it with an aluminum parallel flow. If the condenser is one of the later plate designs, it may not be worthwhile replacing.
  • Add a binary cutoff switch and R134a service ports.
  • And a great deal of work to flush, assemble, test, and charge everything.

Having the right tools is crucial for DIY. You will definitely need a charging manifold, a 2-stage vacuum pump, and a micron gauge. To go 1st class, you will also need a beadlock hose crimper, a flush bottle, and a tank of dry nitrogen w/regulator.

Good luck,

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I’ve never had any success with propane or envirosafe. It does not seem to cool for crap here in Texas. At least with my Mercedes, I see no value in using it over R134a.

You should really flush the old mineral oil if converting to R134a, especially if you have an GM A6 compressor as it has it’s own little oil sump. R134a does not carry mineral oil well and as a result, it will just sit in your system. Too much oil is not good you’ll be amazed at how sludgy your old system can be.

Why do you want to convert to R134a? You will lose some cooling capacity with R134a vs. R12. I find R12, in Tucson anyway, is marginal at best. You can still get R12. It is about $35 to $40 per can on ebay and you need about 3 cans. I doubt that it costs much more to restore the R12 system than to convert to R134a and restore the system.

With a properly charged R12 system operating at the correct suction and discharge pressures, a clean condensor, rebuilt compressor, new evaporator and expansion valve, my A/C worked OK up to about 95 F outside ambient temperature.

If you are working over the A/C system you should change out the hoses whether you use R12 or R134a. After 25+ years the rubber IS leaking.

Dave Christensen
Tucson, AZ
65 Etype OTS
91 XJS Convertible - RIP
12 XK Convertible
12 XJ

Why do you want to convert to R134a? You will lose some cooling
capacity with R134a vs. R12. I find R12, in Tucson anyway, is
marginal at best.

That just means the conversion was done incorrectly. Yes, you lose some
cooling capacity with R-134a, but the A-6 compressor is a 5-ton compressor
driving a 2-ton climate control system. It is SO far overpowered that you
simply should not notice any reduction in cooling. If the vents aren’t putting
out air colder than 40 degrees F 30 seconds after turning the system on and
putting the fans on high speed, there’s something wrong with it.

Biggest problem I had with it was it would cause the rear windshield to fog up
here in the Florida humidity. My rear windshield defroster had some open
circuits in the grid and wasn’t helping. I had to modify the center vent so it
wouldn’t blow frigid air straight back there.

– Kirbert

A6 compressor is used on many European cars that have marginal performance when running R134a.

Condenser and evaporator size are also a factor. If they’re not big enough, you won’t get the heat transfer required to make an efficient system

This was NOT a conversion. I stayed with R12 so I would not lose capacity. I don’t remember the pressures and temperatures now, but they were correct for R12. (I am a mechanical engineer and know how to read a Mollier diagram.) I don’t think I was getting 40 degree air out the vents with 100 F ambient air temp. The condensor fins were clean and not bent/plugged. The expansion valve and evaporator were new and the correct drop in replacements for the XJS.

This was the third XJS that I have had and the cooling on all three started crapping out when it got above about 95 F. I went through everything on this last one (a '91) and could not get any significant improvement over the other two '92s. All three were R12 systems.

Humidity is not a problem in Tucson. It is 81 F and 1% RH here now, which is typical except for our monsoon season.

When my '91 was totaled a month ago I fixed the A/C problem. I bought a '12 XK. Since there is no one on that forum I can’t help myself and frequent this one and the Etype forum. When I get more garage space I will get another XJS. I need a home for my Arizona V12 JAG vanity plate!

Dave Christensen
Tucson, AZ
65 Etype OTS
91 XJS Convertible - RIP
12 XK Convertible
13 XJ

Here is complet set, I have this on my 1988 XJS and working w/o problems.
But it is in UK.


If I may add my two cents on the subject…

Over the past 23 years that I’ve owned my '89 XJ40 I have become (and I say this in all modesty) somewhat of an expert in Jaguar air conditioning systems of that area. Prior to that I also had a Series I XJ6. I’ve completely rebuilt both systems myself and when I say rebuilt I mean I removed EVERYTHING, including the evaporators (which I doubt Indiana Jones could unearth !)

My first observation is that there are two entirely different systems that you’re working with…

  1. the air cooling system

  2. the air distribution system

When people complain that their system isn’t performing correctly the ready answer is to throw in some
Freon (DuPont trade name for R-12) or R134a refrigerant in later (93-94) or converted cars.

You can begin to check if the cooling system is up to snuff with a quality set of air conditioning manifold gauges. The pressures on the high and low side of the system, both static and dynamic, will tell you quite a bit if you know how to read them correctly and factor in the environment your testing in (temp and humidity). But there are also some other gotcha’s like the clutch on your compressor. But lets assume that your cooling system IS chilling your evaporator down to 33/34 deg. does that mean that your home free … not really …

The air distribution system has to get that chilled air to your vents and that may be harder then it looks.
When I recently rebuilt the A/C system on my "89 I found two interesting things, well three really.

The first was that the intake face of the evaporator was almost totally blocked with almost three decades of dust, dirt and debris, along with melted foam. Remember there’s no filter.

The second was that the foam that wraps around the evaporator unit inside the plastic housing was completely gone leaving about a 1/2" gap all the way around. So if the incoming air couldn’t force itself through that nice cold (clogged up) evaporator it simply followed the path of least resistance around the sides of the evaporator through that 1/2" opening.

The third surprise was that both fresh air doors in the two fan units had failed to the outside (HOT) air
position. One doors vacuum actuator was broken and the other door’s actuator was OK but it wasn’t getting any vacuum because of a bad vacuum valve. Geez, what are the chances !!

So I had a perfectly good cooling system but the hot outside air was being blown around it, up through the correctly positioned blend doors, out through the vents and … right into my face. All the R-12 in the world wasn’t going to fix that.

Very nice writeup. I am curious to hear what you learned when rebuilding your series 1 XJ6. I’ve had two, and there’s still some mystery for me in the HVAC system of that car. One pair of parts (little rigid ducts with flapper valves in them) I could never figure out and finally just removed them.

Robert …

Yes they are beautiful cars, love that big front grille. I don’t know why I ever sold mine after almost completely restoring it (actually it was in excellent shape when I bought it, zero rust) but sometimes life just gets in your way.

I regret to say I have no recollection of the parts you’re talking about. That was many years and too many projects ago.

I just did an online search and came up empty handed, sorry.

Thanks for responding. Roger Mabry and I have undertaken a few mods on the S1 AC system, notably fitting a center vent to allow more air flow.

Agreed about the grille…I fitted a Daimler grille that is slightly larger still. Can’t get too much of a good thing. :slight_smile:

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I’m running propane/ butane. Works really good, need less fluid

I’ve heard propane works well and is cheaper but potential for big explosion in front end collision. r134a refrigerant is not flammable. This is why it is illegal to use propane in an automotive A/C system.