We’ve been talking about air conditioning for a couple of weeks now, so if you’re still feeling the heat then it’s time to wrap up the series so you can get out to your garage and put what you’ve learned to good use.
First things first. We learned the theory behind refrigeration and air conditioning, which centers on this wonderfully useful bit of physics: When liquid boils and evaporates into a gas, it expands and cools. This week, we discuss the thing that’s actually boiling and cooling—the refrigerant itself.
As you probably know, matter can exist in three states—solid, liquid, and gas. We’re most familiar with water, which we see as ice when it’s cold, liquid when it’s at room temperature, and steam when we boil it. But in order for refrigeration to work, you need something that has a low boiling point, something that exists as a gas at room temperature and can be easily pressurized into a liquid so that, when it is allowed to expand, it immediately boils at room temperature and cools.
In addition to the low boiling point, there are two other de facto requirements for refrigerant: It shouldn’t be poisonous, and it shouldn’t be flammable. The problem is that some inexpensive available refrigerants—ammonia and propane, for example—are poisonous and/or flammable. Because of this, in the early 1930s, a new refrigerant based on a chlorofluorocarbon (CFC), specifically dichlorodifluoromethane, was developed. It became known as R12 or Freon. When used in refrigerator and A/C systems, R12 cooled incredibly well. And it was safe—neither poisonous to breathe, nor flammable. In fact, R12 was used for many years as a propellant in a variety of aerosol products and sprayed directly into the air, and it is closely related to the halon used in fire extinguishers.
Unfortunately, the widespread use of R12 appeared to be significantly degrading the Earth’s ozone layer, potentially causing a worldwide health crisis. By international agreement in 1987 (the Montreal Protocol), the use and production of CFCs such as R12 began to be phased out, with automobile manufacturers required to stop using it by the end of the 1994 model year. International manufacturing of new R12 ceased in 1996, but existing R12 can still be reclaimed and purified. The manufacture and sale of the small cans of R12 used by hobbyists to “top off” a system also ended, although New Old Stock (NOS) cans of R12 are still privately traded on eBay and Craigslist (I’ll come back to that).
The Internet is a large and often-strange place, and if you want to search for sites that claim that R12 isn’t harmful to the ozone layer, and that the whole thing was a conspiracy by DuPont because its patent on R12 was about to expire, you’ll find them. Both claims are demonstrably untrue.
In the automotive world, the replacement for R12 was tetrafluoroethane, a hydrofluorocarbon (HFC) branded as R134a. Note that R134a is also sometimes called “Freon,” even labeled as such on the can, so it’s best to be clear and use the names R12 and R134a. Because R134a is an HFC, not a CFC (stay with me for a minute), it does not have the ozone-destroying properties of R12. However, there were—and are—some challenges to using it in an automotive A/C system designed for R12. The molecule size of R134a is smaller than that of R12, so there was concern that R134a could leak out through the hoses and flare fittings that R12 systems used. R134a systems operate at higher discharge-side pressures than R12, which can cause compressor seals to leak. Bottom line, R134a simply doesn’t cool as well as R12.
In addition, there was the lubricant issue. Because A/C compressors have moving parts, they require oil. Oil doesn’t stay in the compressor, however, it dissolves in the liquid refrigerant and gets carried through the system as a fine particulate mist when the refrigerant goes through its liquid/gaseous transition. So the oil must be compatible with the refrigerant. R12 systems used mineral oil, but unfortunately mineral oil doesn’t dissolve in R134a. So, along with R134a came a new oil: Polyalkylene Glycol—or PAG oil.
Note that there is another kind of oil called Polyol Ester Oil (POE). The advantage of ester oil is that it works with both R12 as well as R134a, so you can fill the system with it and then use either refrigerant.
Note also that, unlike mineral oil, both PAG oil and ester oil are hygroscopic—that is, they absorb water. R134a reacts with water to form hydrofluoric acid which damages the internal A/C components. This is why it is crucially important that R134a systems be properly evacuated (pumped down to boil off any moisture) and kept sealed.
The problem with R134a conversion
In the years following the switch to R134a, there was confusion over what was required to maintain the A/C of older cars. With new R12 no longer being manufactured, the market price soared to $100/pound. And with R134a costing only two bucks a can, converting to the new inexpensive refrigerant seemed the thing to do. The problem was that there was not agreement on exactly what was required for the conversion. Because the two oils were different, R134a certainly wasn’t a “drop-in” replacement for R12.
Initially, an invasive recipe was proposed: the system should be flushed to remove any traces of the old R12-specific mineral oil, the compressor and expansion valve should be replaced with R134a-specific versions to perform correctly, and the old hoses should be replaced with 134a-specific barrier hoses to forestall leakage. Any old black o-rings should be replaced with R134a-compliant green o-rings. Of course, the receiver/drier needs to be replaced, as it does any time an A/C system is opened. A set of R134a-specific charging port adapters should be installed to eliminate the possibility of refrigerant cross-contamination. The compressor should then be filled with R134a-specific oil (usually PAG oil) and the system evacuated and recharged.
Because this recipe was quite expensive, a backlash developed which gave companies an opportunity to sell “conversion kits” consisting of nothing but the charging port adapters and a small bottle of oil that was somehow magically supposed to make your mineral oil R134a-compatible. A/C professionals derisively called these “death kits” because they had a reputation for causing the compressor to seize a few months later.
Over time, a credible middle ground emerged. As long as the compressor was working well, it could be drained, filled with R134a-compatible oil, and reused. An R134a-specific expansion valve was preferred but not strictly necessary. The concern that the original R12 hoses would leak R134a like a screen door on a submarine appeared to be largely unfounded, as the insides of original hoses seemed to naturally become impregnated with a combination of refrigerant and oil that acted as a barrier. So as long as the system was functioning correctly and not leaking, it appeared that you could flush the system of any old oil, change the oil in the compressor to PAG or ester oil, replace only the receiver-drier and the o-rings, screw on the charging port adapters, evacuate the system, and recharge it with the new R134a, using about 80% as much as the original R12 volume.
The problem in all of this is the sentence “As long as the system is functioning correctly and not leaking.” Who in their right mind would take a tight, cold, R12-based system and convert it to less-efficient R134a? Thus you see how R134a conversion was often applied to systems that were not working correctly, if they were working at all.
Now, in the case of big American cars, with their massively overbuilt A/C systems and huge condensers, R134a conversion often worked fine. But many European cars, such as the vintage BMWs I love, had A/C systems that never functioned all that well even when they were new and charged up with R12. To take one of these and convert it to R134a was usually a recipe for disappointment.
For all of these reasons, the issues of conversion and performance need to be cleanly separated. If an A/C system isn’t working, the root cause needs to be diagnosed, and the system needs to be fixed. If you’re going to go to all that effort on a vintage car with an A/C system that hasn’t been used in years, it usually behooves you do a full-on rejuvenation of the system and replace the compressor with a new compact rotary-style unit, replace the condenser with the largest parallel-flow condenser and big fan that’ll fit in the nose of the car, make all new hoses, and flush the evaporator. You can then add ester oil that’ll work with either R12 or R134a. With a tight modernized system that’ll accept either refrigerant, you should then consider where and how the system will be operated. If the target environment is only moderately hot, and your use of the car is light, R134a will probably be fine. But if you live in a hot climate, want to daily-drive the car, and the car has a tiny-capacity A/C system which, even after modernization, may only perform marginally, you may want to consider sticking with R12. Which brings us to…
The availability of R12
There’s a lot of misinformation surrounding R12. It’s often said that R12 is no longer available. That’s simply not true. Small NOS cans of R12 are widely available on eBay and Craigslist for about $30 apiece. Since these days a can of R134a is about $15, the cost differential isn’t what it was in the panicked days of the mid-1990s.
It’s often said that buying or selling R12 is illegal. That’s not true either. Anyone selling R12 is required to verify that the buyer has an EPA Section 609 certification to work with mobile vehicle air conditioning (MVAC) systems. eBay requires that anyone posting an auction for R12 check that the buyer has that certification, but eBay has no way to enforce it. Certainly no one selling cans of R12 on Craigslist is asking for your EPA 609 card. Also, the EPA 609 certification can be easily obtained by taking an online exam. Note that I am not advocating taking the exam and getting the EPA 609 certification simply so you can legally buy R12; I’m just stating what the law appears to be.
So when someone says, “You can’t get R12 anymore,” or “It’s illegal to use R12,” those things simply aren’t true. You can get it and use it. Legally. The issue is whether you should. And that brings us to…
The real issue with using R12
I continue to use R12 in two of my cars—my 1972 BMW 2002tii and 1973 Bavaria. These are cars with poor A/C reputations, which is precisely why I continue to use R12 in them. I can tell you that R12 is some seriously great refrigerant; it gets both of these cars meat-locker cold almost from the instant the A/C is turned on. (To be clear, both cars also have a new rotary-style compressor and a big parallel-flow condenser and fan.)
But the problem with R12 is twofold. First, it is a pernicious ozone-destroying agent, so if you are going to use it in a car, you are morally required to do everything under the sun to thoroughly leak-test the system before charging it with R12. Unfortunately, taking the longer view of things, even if you do leak-test a car thoroughly and properly all A/C systems leak eventually, so any can of R12 you put into a car will likely wind up in the atmosphere, an eventuality that I am less and less comfortable with.
Second, as you’ll see below, if you have to perform work on an A/C system that has refrigerant in it, it is illegal to vent the refrigerant (to let it escape into the atmosphere); it must be captured and recovered. Very few DIY-ers have recovery equipment (I don’t), so you need to take the car to a shop that does, and fewer and fewer shops keep and maintain R12-recovery equipment. For this reason, when a car is being sold these days, R12 is often seen as a liability, a looming conversion expense, even if the system is functional and cold. I was recently selling a beautiful 1987 BMW 325is with cold R12-based A/C. A gentleman in Canada was very interested until he learned about the R12. He passed. “No one here will work on it,” he said.
Hopefully I’ve properly conveyed that, if the A/C in your precious vintage car is long-dead, the question isn’t whether you choose between buying a few NOS cans of R12 and shooting them in (seriously don’t do that) or “converting” to R134a. The question instead is: Why is the system dead? On a long-dormant system, the odds are very high that it’s dead because it has no refrigerant in it, which means it has leaked out… which means there’s a leak that must be located and fixed. Of course, there could be other problems such as a seized compressor or a blocked expansion valve. Hell, it’s possible that not all of the original A/C components are even there anymore.
The issue is that you need to reach the point where the system is functional and leak-free. As part of doing that, you often wind up replacing major portions of the system—not because that’s strictly required in order to convert it to R134a, but because that’s what you need to do in order to get it functional again. But once you’re on that path, you can improve the system with a new compressor and parallel-flow condenser which, in most cases, will allow you to get good results with R134a.
Yes, there’s a certain irony in the fact that we’ve gone full-circle from the invasive “you’ll need to replace almost everything including the compressor and hoses in order to properly convert R12 to R134a” to “you don’t need to replace all that much; just flush it, new oil, new drier and o-rings,” and back to “you’ll need to replace almost everything including the compressor, hoses, and the condenser.” But this change has occurred both because the cars are that much older than they were when the R12 to R134a change occurred in the mid-1990s, and there is now a better understanding of the need to take advantage of updated compressors and condensers in order to get the A/C systems to blow adequately cold with R134a.
You can look up the law yourself at www.epa.gov/mvac, but basically it boils down to three things. The following bullets are verbatim from EPA’s website:
Refrigerant: Must be EPA-approved and cannot be intentionally released (vented) into the environment.
Servicing: When payment of any kind is involved (including non-monetary), any person working on an MVAC system must be certified under section 609 of the Clean Air Act (CAA) and they must use approved refrigerant handling equipment.
Reusing Refrigerant: Refrigerant must be properly recycled or reclaimed before it can be reused, even if it is being returned to the vehicle from which it was removed.
There is an additional requirement that the car’s A/C have charging fittings that are unique to the refrigerant being used, but it’s the venting part that’s of the most interest, as it’s the area where you can get fined. When R12’s effects on the ozone layer became known and it was superseded by R134a, EPA came down hard with large fines on both professionals and DIY-ers. The following is verbatim from EPA’s website:
“EPA performs random inspections, responds to tips, and pursues potential cases against violators of the Section 608 regulations. EPA is authorized to assess fines of up to $37,500 per day for any violation of these regulations.”
In addition, there is a $10,000 “rat-out” fee your neighbor can collect if you’re venting refrigerant and he tattles on you. I think that, with hindsight, many people would agree that, even given that R12 is an ozone-destroying agent, fines of this level made many hard-working A/C technicians hostile to the government, and thus were counterproductive.
Nevertheless, repeat after me: It is illegal to vent refrigerant. Don’t do it. As I’ve said, R12 is a nasty ozone-destroying chemical and should never be released to the environment under any circumstances, so in addition to being illegal to vent it, you have a moral obligation not to vent it. R134a is not an ozone-destroying agent, but it is a greenhouse gas, and is illegal to vent as well. If you’re resurrecting the A/C in a vintage car, the vast majority of the time the refrigerant has long since leaked out, but if your car has refrigerant in it, and you need to open up the A/C system to work on it, spend a little money and take the car to an A/C shop. Stay on the right side of the law, the environment, and your conscience, and don’t vent refrigerant.
R12 and R134a are not the only game in town. There are other EPA-approved refrigerants such as “Hot Shot” and “Freeze 12,” which you can find here. Each has its own cult following and requires its own EPA-approved charging fittings.
Then there are three new EPA-approved “climate-friendly alternatives.” There is R1234yf, which is already being used on new cars but is classified as “mildly flammable.” At $70 per pound, no one is using it in retrofit applications. There is R744, which is literally carbon dioxide (CO2). Because of R1234yf’s mild flammability, BMW and Mercedes are now adopting R744. However, the operating pressures are reportedly four times those of other refrigerants, so retrofit appears out of the question. And then there is the very interesting refrigerant R152a, which is the ingredient in “keyboard duster,” minus the bittering agent added to prevent inhalant abuse. You can find many videos and web forum posts where people retrofit R152a into cars that originally had R12 and profess excellent results, but it is not approved by the EPA for retrofit applications, only new car applications.
Lastly, there are the flammable organic refrigerants (propane and its blends). To be absolutely clear, these refrigerants are not EPA-approved and shouldn’t be used. You can spend interesting evenings going down the rabbit hole online and reading posts from folks who vigorously defend flammable refrigerants and say, “You do know that your car carries 20 gallons of flammable gasoline, don’t you?” Yes, but gasoline usually isn’t routed through the passenger compartment, and there’s a zero-tolerance policy toward gasoline leakage. In contrast, the most likely reason you’d consider recharging with an “alternative refrigerant” is because the refrigerant leaked out of your car and you’re trying to avoid doing a full-on A/C rejuvenation which includes finding the leak and properly changing refrigerants. I’m not a lawyer, but charging a known-leaky system with something flammable sounds like culpable negligence to me.
With that said, I’ll agree that the flammability issue may not be as black-and-white as it appears. For example, while R12 itself is similar to the halon used in fire extinguishers, when R12 is mixed with mineral oil—the most commonly-used lubricant oil in R12 systems—and aerosolized and burned, it creates phosgene gas, which was used as a chemical agent in WWI.
You can recharge your A/C system with chicken soup (lousy refrigerant, by the way) and no black helicopters will come to your house, but in a world where people usually don’t hold onto their cars forever, R134a is still the best choice for retrofit applications. If you use anything other than R134a, you’ll likely create a situation where you must be the one servicing the system. Even if you’re OK with that, if the system needs work, any refrigerant in it will need to be recovered. Since you can’t vent any refrigerant without breaking the law, and since you’ll be hard-pressed to find a shop that will recover anything other than R134a, you’ll have painted yourself into a corner.
Stay cool, everybody.
Rob Siegel has been writing the column The Hack Mechanic™ for BMW CCA Roundel magazine for 30 years. His new book, Just Needs a Recharge: The Hack Mechanic™ Guide to Vintage Air Conditioning, is now available on Amazon. You can order a personally inscribed copy here.