R12 to R134 conversion
This time of the year and the air con is struggling to cool. The local air con shop says it needs gas but as it is an old R12 system and this gas is no longer permitted, it will have to be converted to R134. Apart from changing the service connections, it will need to flush the system and replace the drier as a minimum. So far so good. However, they also say that all the pipe joints will have to be ptf'd and resealed and it is very likely that the rubber hoses may fail, so better change them now. etc etc.
Another mobile air con outfit says sure you can do this but why bother when you have the option of using the "drop-in" gas which we can supply and regas at your home,
The "drop in gas" is basically a R24 refrigerant derivative- which is legal.
Does anybody have experience of this solution? are there any pitfalls to watch out??
R134a is less efficient than R12, so you will not get the same cooling effect from the same compressor and evaporator. The O-ring seal in the pipe joints will need to be changed also as R12 seals may disintegrate with R134a. Hoses, not sure. I would guess these will be OK. The drier should be replaced anyway every 5 or 6 years.
The required compressor lubricating oils for R12 and R134a will also be different. R134a requires synthetic, compressor, lubricating oils, while R12 will work with mineral oils.
R12 is di-chloro-di-fluro-methane, CFC (aka FREON) and it is now banned due to ozone-layer depleting properties, but it was a very efficient refrigerant.
RS24 is mix of R134a combined with R125 and is supposed to be a 'drop-in' replacement for R12, but I think it's not widely used and will likely be expensive. However, as it contains R134a, I am not sure whether or not seals would still need to be replaced. If the RS-24 mix has the same partial-pressure as R12, then the fill amount will be less guess-work.
Apparently, if you switch to RS-24 (or R134a, for that matter), you need to remove any traces of R12 from the system. Drier should be replaced and system vacuumed for a good hour or so. - see below.
After re-filling, make sure you have a new sticker on the A/C system to show which gas is in there.
http://www.comstarproducts.com/rs-24-refrigerant
Q & A here:
http://www.refsols.com/files/RS-24/RS-24-Q&A.pdf
NOTE these:-
13 Q: Can RS-24 be used to top up a system originally charged with R12?
A: No. Such a mixture can produce extremely high pressures due to the formation of a R12/R134a azeotrope.
17 Q: What tests have been carried out on RS-24 and what are the results?
A: Tests on RS-24 have been carried out in commercial refrigeration, domestic appliances and mobile air conditioning. The results show good oil return to the compressor in all cases and a level of efficiency similar to both R12 and R134a.
Hello leonidas,
Is your truck a W460 ? do you have the add on aircon module below the centre console ? (Webasto, Devavia)
I am interested because i have this module in mine and I was told it would cost the earth to get it serviced and running efficiently and correctly. It does work but the hot setting is warm and the cold is cool if you know what i mean.
How do you envisage the service engineer will test the system for leaks?
I had aircon in my last MB 124 estate and engineer tested for aircon leaks using some sort of light (might have been UV but not sure).
That was about 10 years ago so things may have moved on from then or that method might not work on all gases.
Big leaks will be detected when vacuuming-down the system, prior to refilling. Small leaks may not be detected until you've lost pressure a few weeks or a few months down the line. However, a new charge of refrigerant is usually accompanied by a small injection of fluorescent dye, which can then be detected with a UV lamp, as Mark pointed out, in the post above. Static pressures will be around 80 psi and operating pressures up to 250 psi, so a microscopic leak can reduce the amount of refrigerant over many months. The hose and pipe connections tend to be clamped flanges sealed by O-rings. Either the O-rings fail, or pitting corrosion on the flanges (road salt etc), eventually prevents proper sealing. Also, the evaporator and condenser are delicate and can easily develop leaks. The compressor should be operated at least once or twice monthly to keep its seals lubricated. if they dry out, that will be another source of leaks.
Leak sealers can also be added with the refrigerant charge.
If you wish to know more, see here:
http://aircondition.com/tech/questions/82/Troubleshooting-with-Gauges-FAQ
Hi Neil,
No, it is a Ge300 ,463 series J Plate and the aircon is factory fitted. It sounds like yours needs re gassing.
Converting to the R134 gas, I was quoted a range of prices spanning from £200 to £400. Re charging alone varies to around £80, but it cannot be done unless the service points are changed from R12 fittings to R134, will need new drier, possibly hoses, etc etc which adds up at the end the cost. Thus the decision to go for the "drop in" solution, which effectively means the use of the alternative refrigerant RS 24. Recharging with RS24 is more expensive than the R134, as far as the cost of gas is concerned, but provided that there are no leaks in the system, there will be no loss in efficiency and no need for a new compressor. I'm having this job done at home next week by one of these mobile outfits and I'll let you know how it went.
leonidas,
Thank you !
I was also searching around to find solutions and did find a guy operating in my neck of the woods offering mobile aircon repair/re-gas and servicing solutions. My fear is that my system being antique 1986 that it will require much work to bring it upto full operating standards.
As always the list is endless and i have a few priorities before embarking upon the resurection of this Diavia system. BUT it's on the list.
Good luck with yours buddy and keep us updated.
Some years ago with a 86 300e in the USA the cooling was rubbish in south Florida summer on newer stuff. The independent Merc guy got hold of R12 and the difference was unbelievable - was told that the military still used R12 and the stuff was available but at a price. I could never get the newer refrigerant to cool properly in a hot climate. The other problem with Mercedes AC - at least the 300e was the AC evaporator was put in and the car built around it
Hi Neilmarton,
I thought you may be interested to hear of the outcome of the conversion from R12 to RS24.
It started by testing the system for leaks and functioning of the compressor. Both found to be OK. There was a small amount of R12 still left in the system but not enough for proper functioning. Then the old gas R12 was removed via a vacuum pump and the system was flushed under vacuum for about 45 minutes. After that the system was re charged with RS24 gas plus an oil additive ( which I was told is useful for maintaining the seals supple and for tracing / sealing leaks - something like radweld) - and tested for about 30 minutes for operation via thermostat settings and temperature drop. With ambient temperature 24 deg C, with temp switch full on, the vent fan at position 3 and air re-circulation switch ON ( i.e. drawing air from the vehicle cabin) - the air outlet temp dropped to 8 deg C. The same 8 deg C temperature was maintained when drawing air directly from outside.
I observed that the return is cold, the a/c Compressor is now running cool , whilst previously when there was very little gas in the system it was running hot to touch, and the air cooling electric fan cutting in and out as necessary. No modification to the service ports or replacement of the drier was deemed necessary.
All above was carried out at home by a mobile service and there was no need to leave the car unattended at any time. I can confidently say that I did not notice any difference in the performance of the system when it was running fully charged with R12 and now with RS24.
I was also told by the service engineer that the RS134 gas is now becoming obsolete as it is being replaced with a different refrigerant. Thus, it may be worthwhile to check and ask questions before committing to modify the system to use R134 .
I hope you may find this of help.
Hi Leonidas,
That's good news and i'm pleased to hear you'll be nice and cool during this little UK heatwave (If it comes)
Thank you ! Yes that is very useful and means there is hope to resurect my AC system ! (I will begin talks with local mobile AC engineers down my way and see how i get on)
Best wishes,
Neil.
Better get your skates on - forecast is for 84o F on Wednesday.
Air con on my G is worked by pressing a button on the roof.....Further temperature reduction can be effected by buttons on the central console that allow air in from both passenger and driver side 
Buttons ? are you showing off ?
Buttons ? are you showing off ?
Oh yes....a huge upgrade from those windy things....
Ah, now I understand why you need the TT upgrade.
You're driving along with all your "aircon" in operation.Well known that this can play havoc with performance figures.
Ah, now I understand why you need the TT upgrade.
You're driving along with all your "aircon" in operation.Well known that this can play havoc with performance figures.
Nah....I need the upgrade 'cause I'm rapidly becoming an expert on the growth rates of grass verges....
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Hi Arnie,
Many thanks for a very thorough response. I guess going down the R24 route there will be no need to change the service points, as in the case of repalcing the system for R134.
How do you envisage the service engineer will test the system for leaks?
Will this be done before charging the system with the new gas?? ( assuming that there is still sufficient R!2 refrigerant left)-
or afterwards?