R134a and R12 Seals, difference?

[Z2TT]

Hello,

I've contacted many A/C Places about retrofitting to R134a and most say that a new reciever/drier has to be installed, system flushed and compatible oil used.

Some articles I have read online say that the new gas (R134a) will eat up the current seals as they are not compatible. Is this correct?

Thanks.

[Nacho]

What kind of car you're planning to retrofit?

[Z2TT]

I'm not planning to retrofit a car, but I'm just curious as to whether seals in R12 systems are
incompatible with R134a, as in the gas will eat them up which is what some people say.

[Nacho]

They will not be necessarity eaten up. Some compressors withstand the conversion quite well.
We used a lot of band new Sanden intended for R12 by just replacing the oil.
Exeptions are the old, pre-1994 Ford FX15 and the GM R4. Others may require replacement of the refrigerant control valve (GM's V5).

[Z2TT]

Thanks,

I've also been told that All Seals, Even compressor seals, and even ALL HOSES need to be replaced.
Why would all Hoses need to be replaced aswell?

[ACProf]

R134 molecules, which are smaller than r12 molecules, will seep through R12 rubber hoses. R134 hoses have a much different layered design including an internal mesh fabric and are called "barrier hoses". If you don't change the hoses, your AC system will need to recharged every year.

R134 reacts with certain components of "rubber" or "neoprene" seals that are quite happy in r12 systems and causes them to deteriorate. When retrofitting to R134 its always best to replace all the orings and seals with R134 (colored green) compatible HNBR (Hydrogenated Nitrile Butadiene Rubber) material.

Lots of questions for not "doing" anything. Sounds like something in the works. Conversions are not as simple as the guy at the auto parts store would make it seem. Do your own research on "R134a conversions" here and on the web.

ACProf

[Z2TT]

Thanks ACprof and others.

Is it the actual gas in R134a that reacts with the rubber seals and deteriotes them, as I have read that it's the PAG oil used with R134a that causes them to swell. I was misinformed that the green seals were Neoprene. I am retrofitting my older car, so I have decided to replace the seals everywhere with HNBR seals (Green). Weird thing is One of the bags of O-rings that I got sold were black, however the shop said they are made of the same material as the green ones.

From what I understand, R134a Can actually leak through the wall of the rubber hose (correct me if I'm wrong), my rubber hose wall is pretty thick (8mm). Excuse my ignorance here, but can R134a Penetrate through that wall and slowly seep out? (not make a crack), but slowly seep out. And is this the reason for the barrier hoses?

[ACProf]

Yes.

[test specimen]

R134 molecules, which are smaller than r12 molecules, will seep through R12 rubber hoses. R134 hoses have a much different layered design including an internal mesh fabric and are called "barrier hoses". If you don't change the hoses, your AC system will need to recharged every year.

R134 reacts with certain components of "rubber" or "neoprene" seals that are quite happy in r12 systems and causes them to deteriorate. When retrofitting to R134 its always best to replace all the orings and seals with R134 (colored green) compatible HNBR (Hydrogenated Nitrile Butadiene Rubber) material.

ACProf

Prof, I'm not sure where you got the information that R-134a is smaller than R-12. It is actually slightly larger than R-12, which makes sense when you know that R-12 is a single carbon molecule and R-134a is a two carbon molecule. I have the diameter of some common refrigerants and water as follows in Angstroms:

H2O 2.68
R-22 4.79
R-12 5.09
R-134a 5.24

I also think you are being too loose with terminology when you say the R-134a 'reacts' with components of the rubber formulations. The things that happen when rubber formulations are exposed to refrigerant and lubricant consist of either swelling or leaching of the rubber formulation. You might have the refrigerant dissolve into the rubber and cause it to swell which degrades the mechanical properties of the o-ring. The oil is less likely to dissolve into the rubber because it is a much larger molecule (about 5 to 10 times as large as refrigerant), and is much harder to get in between the rubber molecules.

You may also get part of the rubber formulation to dissolve (leach) into the refrigerant and lubricant. Short fragments of the rubber caused by the heat given off by mechanical mixing of the o-ring formulation (mastication or compounding) can be removed from the o-ring and cause shrinkage. If the o-ring is formulated with extender oils to soften them, the extenders may be leached out of the o-rings as well. Most A/C o-rings do not use extenders.

In reality, both swelling and shrinkage happen at the same time. There was an ARTI MCLR research project done at the University of Akron devoted to understanding how various types of rubber (elastomers) behaved in refrigerants and lubricants done in 1993. This report is a good resource to show the actual effects of refrigerant and lubricants on base rubber and formulated products, and I think it can be found on the web at a US DOE site. It showed that R-22 and mineral oil were the most aggressive refrigerant / lubricant combination to most common elastomers. R-134a was only highly aggressive towards Viton based materials.

Another issue as to why HNBR is preferred has to do with compression setting. Over time an o-ring becomes set in a shape, and is no longer as flexible as it once was. Higher temperatures cause compression set to happen sooner. HNBR has better compression set performance than either neoprene or nitrile (NBR) rubber, so performs better over time. During a retrofit, replacing older compression set o-rings with newer more flexible o-rings will result in less leaks, regardless of o-ring type.

BTW, the rubber itself is basically colorless, so the green is from a colored material added to the formulation. The black is normally from carbon black added to the formulation for mechanical strength. HNBR , neoprene or NBR can be made into almost any color.

The nylon barrier layer in the R-134a hose was moved to protect the other rubber layers from the PAG lubricant. There were R-12 nylon barrier hoses used in the late 1980s and early 1990s where the nylon layer was internal to the hose structure, but in the R-134a hoses the nylon layer was moved towards the inside of the hose. The nylon layer really slows down the migration of refrigerant through the hose. The butyl rubber layer on the outside of both the R-12 and R-134a hose is to slow down the ingress of moisture, while the braid is to provide mechanical strength.

[ACProf]

Test Spec,
Thanks for taking the time to give us all some definitive answers to some fleeting questions. My statements have come from "knowledgeable and reliable" sources whom I believe to know what they're talking about from their training, credential, and experience, some personal, some professional, and some from professional organizations posting on the internet.

I'm getting ready to fold up my tent. Auto A/C is getting to be too much tool and equipment inventory to keep up these days. I have to make a choice if I'm going to buy an upgrade for my PC OBDII system to read the new CAN bus on the new cars. Probably not!

ACProf

[Z2TT]

Thanks test specimen,

I have always been told and read everywhere that the R134a molecule is much smaller, being the reason why R134a leaks out so much quicker than R12. So in fact it is bigger, does that mean R134a has the likeliness to leak out at the same rate as R12? I don't understand what is the reasoning behind people saying the R134a molecule was much smaller, I always thought it was too from reading it over and over again. Even refrigeration websites, refrigeration organizations state as well that the R134a molecule is smaller. Such as the following websites

http://cienbas.galeon.com/02one_component.htm
"R134a molecule has smaller size than R12 molecule which makes danger of leakage more considerable"

http://www.sdm.kiev.ua/eng/refregerants ... -134a.html

I have even seen this in books, such as "Automotive air-conditioning and climate Control systems"

http://books.google.com.au/books?id=b92 ... ze&f=false

Has a lot of technical information about different types of refrigerants, and it states that R134a has a smaller molecule size than R12

As for the Nylon barrier protecting the Rubber hose from PAG oil, does PAG oil degrade the Rubber hose very quickly as opposed to Mineral so is that the reason for the Barrier? Then that would help prevent leaks from the hose right? since the barrier protects the rubber from the PAG, and if the nylon were not inside the PAG would degrade the rubber quicker and cause a leak?

Thanks Again

[Tom Greenleaf]

Z2 -

Who is going to read the whole web? Cut out what you want to not whole websites!

T

[Z2TT]

Sorry my mistake, I meant to say webpages, those links are to the actual page, not the main sites.

Thanks.

[Tom Greenleaf]

THIS IS A FREAKING WEB PAGE! WTF do you want?

T

[Z2TT]

Hi,

I put a quote under the link quoting text from the web page, is that better?

[Tom Greenleaf]

Just doing my job for free at that! No links allowed unless I'm otherwise instructed.

Relax! I don't make a dime and spend hours here and elsewhere sites.\

T

[test specimen]

Thanks test specimen,

I have always been told and read everywhere that the R134a molecule is much smaller, being the reason why R134a leaks out so much quicker than R12. So in fact it is bigger, does that mean R134a has the likeliness to leak out at the same rate as R12? I don't understand what is the reasoning behind people saying the R134a molecule was much smaller, I always thought it was too from reading it over and over again. Even refrigeration websites, refrigeration organizations state as well that the R134a molecule is smaller. Such as the following websites


As for the Nylon barrier protecting the Rubber hose from PAG oil, does PAG oil degrade the Rubber hose very quickly as opposed to Mineral so is that the reason for the Barrier? Then that would help prevent leaks from the hose right? since the barrier protects the rubber from the PAG, and if the nylon were not inside the PAG would degrade the rubber quicker and cause a leak?

Thanks Again

Here's my guess as to why so many people have got it wrong on the molecular size: They are confusing molecular weight with molecular size. The molecular weight is 120.9 for R-12 and 102.1 for R-134a, so it seems like R-12 is bigger than R-134a, but molecular weight is not the same thing as molecular size. The configuration of the molecular structure and the bond length between all the atoms in the molecular determine the molecular size. The molecular weight is determined only by the empirical formula of the molecule.

I got my molecular size data from a physicist at a refrigerant manufacturing company, and this data is used by the people who create molecular sieves for refrigerant drying so they can design the correct pore size in the sieve to hold water and exclude refrigerant. I can't speak for where the other people came up with their determination that R-12 is larger than R-134a.

The PAG will only very slowly degrade the rubber, but from a hose manufacturers view, it will affect the strength of the hose during the life of the vehicle. It seemed to be a relatively quick and easy change to move the nylon layer to provide more protection for the rubber layers. I don't think the R-134a / PAG in non-barrier hoses was any kind of major leak problem, as evidenced by retrofitted hoses from R-12 / mineral oil systems holding up well as long as the rubber was saturated with mineral oil prior to the retrofit. It turned out the mineral oil adsorbed into the R-12 hoses provided a good barrier to the R-134a, and cut way down on the leak rates for R-134a after retrofits. The retrofit hoses saturated with mineral oil were not as good as a true barrier hose, but they work well enough.

There isn't much publicly available data on hose leak rates, and I am remembering the data my company generated to support R-134a retrofits back in the early 1990s. We actually measured the leak rates of 'normal' hoses and barrier hoses, in retrofit and OEM uses. The hose test was done in a sealed box at controlled temperatures with hoses pressurized with refrigerant. We measured the concentration of refrigerant in the box to calculate the leak rates per square meter of hose surface.