Hi all,


My 1990, XJS 3.6 has never had functioning aircon since I bought it 3 months ago. It was laid up for 10 years so I am guessing there is little or no gas in the system.


I know that this could work out mega expensive but as a first try I was going to get the system re-gassed just to see what happens. I understand that the cars originally used an old type of aircon gas that is no longer available for environmental reasons.


My question is can modern aircon gas be used in the original Jag aircon system or do you have to change any of the hardware before re-gassing with the new stuff?


Thanks,
LeeP

 

Not sure about the UK but in the 'States the alternative is R134.....

Opinions and experiences vary quite a bit. Some have simply evacuated the system and installed R134 with the correct oil.....and claim to get good results.

Others clam that, at minimum, the o-rings and dehydrator must be changed. Still others insist on new hoses.

But as far as 'hardware'-- compressor, evaporator, condenser, metal pipes, that sort of thing----you shouldn't need to change any of it.

What does your air conditioning guy say?

Cheers
DD

 

Hi Lee

The old type refrigerant was stuff called R12 which was phased out in 1993 and as Doug said was replaced by R134 (or R134a to be exact)

Air Con: Anti Bacterial Clean and Re-charge, could set you back about £60

But before you get into that, you might want to replace that Spark Plug, that's hiding underneath the Air Con Compressor (or preferably do all at the same time)

 

You do NOT need to have your air conditioning system converted to R134a gas!

There are several drop-in R12-equivalent gases which are legal and easily obtainable (in UK). KWE use RS24, also known as Isceon MO49 or R413

 

Lee


You must replace the dryer (only about 30 quid). The best thing is to ask an aircon specialist to test for whether the system will hold a vacuum/hold pressure, before spending money on new gas.


If the system will not (highly likely) then finding the leaks has to be done. very likely leak culprits will be: the compressor seals; the flexible hoses. For these you are looking at 350 quid or so and you will be very fortunate if they are not leaking. Less likely places for leaks are the condenser radiator and the interior evaporator on the aircon unit. The former is an easy change but around 200 quid from memory; the latter a major pain as the dash has to come out.


Once the leak situation is established and fixed if needed, your only remaining worry will be the functioning of the electronics in the unit in the dash, which realistically can only be tested by seeing what it does when the system is gassed up.


Greg

 

I took mine into ATS at Carshalton for 134, he vacuumed it for 30 mins and re-gassed it, total price was £36.00 with over 60s discount, I did change the dryer and expansion valve before hand, although over the years there is nothing on the aircon I haven't replaced except the steel h.p. pipe and silencer,

 

KWE have a great article recommending RS24. However, RS24 is in fact a blend of two different gases with HFC134a comprising the significantly major part ! So if 134a is going to pass through the hoses so is the 134a component of RS24 !

However, the RS24 blend has two distinct advantages.

It will work with both R12 oils and PAG oils used only with 134a so you can gas up and your agent can insert PAG150 oil as the A6 compressor needs and you don't have any problem about older mineral oils still running around the system.

The biggest advantage is that the performance characteristics are closer to R12 than 134a are. 134a is less dense and works at a higher pressure. The evaporator and serpentine condenser on the XJS are designed for R12 and so the minimum temp of air off the evaporator is higher with 134a than it was with R12. The cold air comes off slightly warmer. RS24 is far closer to R12 as you can see here
rscool.com : RS-24 (R-426A)

However, for the last 10 years my car has been filled with 134a, as I changed the compressor and condenser this year I went to all the trouble of an RS24 refill. Finding someone with stock was quite a game. Then he wanted to fill it at 70% of mass of R12. With the system still significantly under-performing at that point he put some more in. I did not have data to hand. when I got home I checked and the rule of thumb is 90% by mass and he had put in slightly less than 90% of the minimum charge (in fact from the data sheet 102.6/120.9 so 91% ) So I took it back and he begrudgingly put in some more to make it about 90% of the mid way point between min and mean charge.

I have yet to stick a temp probe on the output but my take on it is that for a UK climate the extra performance of RS24 will make no worthwhile difference. In the states or southern Europe then there is case to be made. I have just come back from the South of France and on the hottest day around 34°C coming to the car after it stood hours in the sun, the air con had cooled the cabin in a very short time., after all this is the unit for the 4/5 seater sedan.

Now that leaves us with migration rate through the hoses. My car did 2005 to 2012 on one shot of 134a before it needed a regas. What was the quality of hoses on the XJS ? No idea but I just think I will get some hoses off a scrapper and get them fitted with super-dooper 134a resistant hose and then come next re-gas time get them swapped.

My biggest concern is looking in the sight glass. There are arguments all over the internet about the irrelevance of a sight glass for 134a. There are "globules of ester oil or PAG oil that will look like bubbles" (I don't think they do) and "it is ok to have bubbles in 134a" type answers. The basic fact is bubbles of gas are bubbles of gas because at that temperature and pressure the molecules have too much energy to be liquid, so either the pressure needs to go up or the temperature down. That is a basic law of physics. But since the sight glass is post condenser there is not much chance of cooling before the expansion valve and the pressure is not going to change so bubbles are just another sign that the condenser was not large enough given RS24 or 134a and the evaporator is going to underperform as a consequence. Putting more gas in will reduce the bubbles as the total system pressure will increase but then it might result in early failure of the compressor seals and poor efficiency of the compressor (leaking past the cylinders).

I would very much like to know what AC experts think is an appropriate level of bubbles in an R12 system working with RS24 or 134a. Certainly it is nothing like the "clear liquid" that would be evident in a sight glass when the system was fully charged with R12.

 

RS24 is 93% HFC134a, 5.1% HFC125, 1.3 Butane R-600 and 0.6% Iso-butane. The 134a is a smaller molecule than the R12 CFC.

 

I've done a fair bit of AC work to my cars, and I found it worth while investing in the tools. A vacuum pump and the proper gauge set isn't that expensive. When chasing leaks it pays for itself very quickly. I have changed O rings many times, then pulled vacuum and found the system didn't hold vacuum and then found another leak. I'd not want to have to pay a shop to do this.


When using refrigerants the system wasn't designed for I don't go by weight, but rather by performance. I put a thermometer in the dash vent, set the temp to full cold and fans to maximum. Then I charge in refrigerant and watch the air temperature fall. At some point it will reach a minimum and then start to increase. That is the point where the system is perfectly charged. I also run a garden hose spray over the condensor to remove as much heat as possible to determine the true state of the system.

Some cars have a thermal switch in the evaporator that will cut out the compressor to prevent the evaporator from freezing. As I charge, I'm also watching the compressor. When the temperatures come down and it starts cycling on and off then I know I have the right charge. If the temperature comes down and the compressor is running continously, then it is still under charged. Then vent temp probably won't come down much anymore at this point, but adding refrigerant will help the performance. You still have to watch the system pressures too!

The ideal situation is to have the entire evaporator filled with boiling, liquid refrigerant, but not having any of that liquid escape and go back to the compressor. If the evaporator is only half filled with liquid then it isn't able to remove as much heat as possible, as it is the state change from liquid to gas that requires heat from the cabin to boil the liquid. On cooler days that will probably work fine, but when it gets really hot and maximum heat removal is called for the system won't be able to cope. Think of it like having the throttle only able to open halfway. In most normal driving you wouldn't notice, but when you need to merge quickly then you will see it.

 

Ignore the sight glass. Go by pressures and the vent temperatures, that will tell you all you need to know.

 

It was observations and the fact that the shop manager's boy was asking the boss, who was not taking much interest in the job was suggesting it needed more in, that caused me to go back and ask for the extra charge. Previously at idle on a not too hot day (23-24°C) on max cold the compressor would cycle. It was on full time with the initial charge. With the extra charge on a similar day, the output felt colder and the compressor cycled. On the hottest day I have experienced this summer with the extra bit of charge, the compressor seemed to be engaged all the time at idle but increase the revs a bit and it cycled in and out. So I think that just about matches your advice. It is probably just about there 995 g of RS24.

The Delanair Mkiii system has an evaporator compressor cut out switch. On the XJS & series 3 XJ saloons it is just a single setting but the same system in the XJ40 it has three temp settings to provide for differing amounts of moisture extraction so that contact lens wearers could alter the "humidity" of the air into the cabin.

 

A big collective thanks guys.


As I suspected there is more knowledge in this forum than in many air con companies.


Looks like my plan is a vacuum test to see how bad things are! If it passes this then I will buy a new receiver drier. SNG Barratt list CFC free for a £100+ and non CFC free for £34. Presumably I need the latter if I am to go for an R12 drop in replacement? Then finally a re-gas with RS24 or equivalent.


I will let you know how I get on but for the moment sorting out my non ALBS will have to take priority.


Once again, thanks,


Cheers,


LeeP

 

Sounds like you have it about right. On my 94 in similar temperatures the coldest I can get out of the vents is 6°C air. I also have a Daimler DS420 limousine with dual air front and rear. The rear system is much more effective than the front (as you would expect) and I kept adding refrigerant to get the front cold. I eventually got it down to 3°C, and then checked the rear and it was -19°C! Oops. No thermal switch there!

Minimum temperature achievable will depend upon a number of things, such as the type of expansion device ( expansion valve, oriface, thermal valve) outside temperature, airflow across the condenser, and the condition of the heater box flaps.

On my Saab 9-5 the heater box drum seals are not sealing, so air is bleeding through the heater core before going to the evaporator and the coldest air I can get is 18°C! The fix is a new heater box ($900) and the dash out (12 hours labour) so I said forget it. It's a winter car anyway and the heater works well. The XJS is the summer car so I don't care about functioning AC in the Saab. It's amazing how the V12 is so much easier to work on than the Saab V6. I never would have thought that; the V12 is actually quite mechanic friendly.

 

I did not make it clear, the evaporator sensor that cuts out the compressor is a temperature sensor. So minimum outlet temperature will not reduce once the system is at the point of cycling, dropping out the compressor and re-engaging it. As you say Jagboi, min output temp is then at the mercy of heater box condition and the vacuum water valve working (Mk 2 & Mk3), so there is no pick up of heat from the core. Flap leakage past the seals is a significant issue for the Mk2 but the rotary flaps in the Mk3 are excellent, the foam covered in a brushed nylon covering which does not seem to degrade like the uncovered foam.

I finished the summer vacation with a long drive (500 miles) from the south of France. Started just after noon with the hood down and drew lots of admiring glances. Mid afternoon and we were were on the autoroute and wanting to pres on so the hood came up. Hot day. I then put the climate control on, with auto temp management. For most of the journey the system was gently hunting in that part of the cooling load cycle between face level vent open and closed. The vacuum delay due to the restrictors in the line caused this modest "hunting" effect to be un-noticed by my wife. When we got out at the services, wow did it feel hot outside. Since the "open face level vent" is some good way from "max cool" on the duty cycle, it confirmed that there was plenty of capacity left in the system for maintaining climate control rather than having to go full cool. Since the motorway was boring I put a watch on a couple of cycles (things petrol heads do !) About just over three minutes from starting to open face level vent to open, close and then about to open again. but as I say, all so gentle and graded that the change was barely discernible.

Thanks for the advice on buying my own gauges and vac pump and doing the basics rather than paying shop prices. Ebay is great isn't it. Just over £100 gets a new Vac pump and set of gauges ! Well worth it.

 

That's far to expensive for the drier, shop around

 

Reading that post that said coolest air at the vent was 6°C I managed to borrow some multiple temp sensors from work, with accuracy to ± 0.1°C. On the evening I tested it was only around 18°C. At idle on max cool the compressor was cycling. It would cut out with vent air at 2.4 to 2.6 °C and then cut back in when vent air had risen to 5.2 to 5.7°C . I dug out on the internet the original Jaguar Service Dept instructions for converting from R12 to R134a. They only want access ports, oil drained and replaced, new O rings and receiver drier and refrigerant changed and make no mention of problems with hoses or seals. However they do say fill with 1150 g of R134 which comes out very close to the 2.5lb charge weight of R12, which is not what GM put on their service bulletins for conversion or is generally accepted.

 

Did they specify Ester or Pag for the oil and how much? It is my understanding that generally converted systems go with Ester. Would you mind posting the instructions?
Thanks

 

"Page 4 "As proven during exhaustive testing, it is possible to have more than the stated volume of oil in the air-conditioning system ie it is permissible to have a Sanden compressor with 135 ml of ester oil plus up to 50% of residual mineral oil. however always attempt to remove as much the mineral oil as possible."

Page 3 "Ester oil RL 100"

I currently keep getting "upload errors". I will try the upload somewhere else. It is 6.42 MB will that upload ok ?

 

Ive sent you a pm with my email if thats easier

 

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