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Showing posts with label car refrigerant. Show all posts
Showing posts with label car refrigerant. Show all posts

Saturday 27 June 2015

R-12 to R-134A Refrigerant Retrofit

R-12 to R-134A Refrigerant Retrofit



R-134a Retrofit


If you drive an older vehicle (pre-1994), the air conditioning system contains R-12 refrigerant (Freon). As long as the A/C system has no leaks and it cooling normally, there is no need to convert from R-12 to the new "ozone safe" R-134a refrigerant. But if your A/C system has lost it's charge because of a leak, collision damage, or the need to open it to replace a compressor, hose or other component, you may have to convert from R-12 to R-134a when you recharge the system
Why? Because R-12 is no longer produced in the U.S. Supplies of recycled R-12 still exist, and some R-12 is still brought in from offshore suppliers. But it is hard to find and expensive. That's why many people simply recharge their older R-12 air conditioning system with R-134a after repairs have been made.

R-134a Retrofit Conversion Costs

Does it make economic sense to retrofit an older vehicle to R-134a if the A/C system has lost its refrigerant charge or needs major repairs? The older a vehicle gets, the more it depreciates. By the time it is 15 or more years old, it may only be worth a few hundred dollars. Many owners will not put any more money into an older vehicle unless the repairs are absolutely necessary to keep it running. Even then, it may be less expensive to get rid of the vehicle or to junk it than to fix it up. Even so, A/C is something that's hard to do without especially during hot weather. Hot summer temperatures and high humidity can make driving in city traffic unbearable.
A professional retrofit by a repair shop can cost hundreds of dollars, depending on what they do. But on many older vehicles, you can save money and do the job yourself - if you have some know-how and the right equipment.

WHEN R-134A RETROFIT MAKES SENSE

There is NO reason to retrofit a vehicle to R-134a as long as the R-12 system is cooling properly and contains a normal charge of refrigerant. A/C systems designed to use R-12 will cool best when charged with R-12 refrigerant. Even if the system leaks, repairing the leaks and recharging it with R-12 is usually the best repair alternative. Converting to R-134a typically reduces cooling performance somewhat, and may require some additional modifications depending on the vehicle model year.
Where retrofit makes the most economic sense is when an A/C system requires major repairs such as a new compressor, condenser or evaporator.
The average repair bill to retrofit when other A/C repairs are needed, according to the Mobile Air Conditioning Society (MACS), is about $100 over and above any other repairs that may be needed (such as replacing the compressor, condenser or evaporator, etc.). The cost to retrofit usually does not add that much to the total repair bill because converting 1990s vintage vehicles to R-134a in most cases is fairly easy and does not require many (if any) changes. If the vehicle has barrier style hoses and the compressor and seals are compatible with R-134a, the only thing that has to be changed is the compressor lubricant.

TWO WAYS TO DO A R-134A RETROFIT

A retrofit can be done one of two ways. The first is to follow the vehicle manufacturer recommended retrofit procedure. This generally involves removing all the old mineral oil from the system, replacing the accumulator or receiver/dryer with one that contains X-7 desiccant, replacing O-rings (if required), installing or replacing a high pressure cutout switch (which many shops seem to forget), changing the orifice tube or expansion valve (if required), then adding the specified PAG oil and recharging the system with R-134a. On some applications, installing a more efficient condenser may be recommended for improved cooling performance. After the modifications are made, the system is recharged to about 85 to 90% of its original capacity with R-134a.
Federal law also requires the permanent installation of R-134a fittings on the high and low service ports to reduce the chance of refrigerant cross-contamination the next time the vehicle is serviced. Labels must also be installed to identify the system has been converted to R-134a.
R-134a service fitting adapters
Installing service fitting adapters allows R-134a to be put into a R-12 system.
The other approach to retrofit is the "quick and cheap" one. On many 1989 through 1993 vintage vehicles, R-12 A/C systems can be converted by simply recovering any refrigerant that is still in the system, adding POE oil (which is compatible with both types of refrigerant), and recharging to 85 to 90% capacity with R-134a.
A simple retrofit may therefore cost no more than a few cans of refrigerant and some compressor oil -- provided there's nothing else wrong with the A/C system. But simple low cost retrofits may not give the best cooling performance, and may not even be possible on some vehicles. Any compressor that has Viton seals is not a candidate for retrofit. This includes original equipment compressors such as Tecumseh HR980, some Keihin compressors and some Panasonic rotary valve style compressors on older Japanese cars. On these, the compressor must be replaced.
Compressor durability is also a concern with some vehicles. Because R-134a raises compressor discharge pressures and increases the compressors work load, some lightweight compressors may not be rugged enough to tolerate R-134a over the long haul. This applies to the Harrison DA6 and Ford FX-15 compressors. The Harrison DA6 can be replaced with a HD-6, HR-6 or HR-6HE compressor. The Ford FX-15 compressor can be replaced with a FS-10 compressor.
Regardless of which retrofit method is used, cooling performance will vary depending on the design of the system. As a rule, expect anywhere from a 3% to 15% decrease in cooling performance when an R-12 system is converted to R-134a. Systems with relatively large or efficient condensers will experience less of a drop in cooling performance with R-134a than those with smaller or less efficient condensers.

ADDITIONAL R-134A RETROFIT TIPS

One way to improve cooling performance when retrofitting an older R-12 system to R-134a is to install a "variable valve" orifice tube in place of the standard fixed orifice tube. These aftermarket variable orifice tubes allow the flow rate through the valve to change for better cooling at idle and low speeds. Such a valve can lower the A/C outlet air temperature by as much as 5 to 8 degrees, which can make quite a difference if the vehicle is crawling along in stop-and-go city traffic.
Adding an extra cooling fan can help boost cooling performance, especially at idle and low speeds. Many older rear-wheel drive cars and trucks do not have a separate electric fan for the A/C condenser. They rely solely on the belt-driven fan for cooling, which may not be adequate in extremely hot weather with R-134a. Installing an auxiliary fan that comes on when the A/C is turned on give provide the extra airflow needed to carry away the heat.
Installing a larger or more efficient condenser can also help compensate for losses in cooling efficiency with R-134a. If the original condenser or evaporator is being replaced because of a leak, damage or defect, make sure the replacement unit has the same or better BTU rating. Some aftermarket replacement condensers and evaporators may not deliver the same cooling performance, and create a problem you did not have before.
When a compressor fails, it can throw metallic debris into the system. Most of the junk ends up in the bottom of the condenser, but some of it can also be blown back into the suction hose. Flushing the condenser, hoses and evaporator with refrigerant or an approved solvent may remove most of the debris, but parallel flow condensers cannot be flushed effectively. Replacement is often recommended if debris is found in the system. Most experts also recommend installing an in-line filter (high side and/or low side) to protect the replacement compressor and orifice tube or expansion valve. There are also filter screens that can be installed in the suction line to prevent any debris from reentering the compressor, too.

ALTERNATIVE REFRIGERANTS

The vehicle manufacturers still do not approve of any alternative refrigerants other than R-134a for retrofit, though a variety of alternative refrigerants currently meet the EPA SNAP (Significant New Alternatives Policy) rules for environmental acceptance. Most of these are blends that are formulated to replace R-12 in older vehicles.
It is important to remember that R-134a or any other alternative refrigerant cannot be mixed with R-12 or used to top off an R-12 system. If an A/C system still contains any R-12 at all, it must be removed using approved recovery equipment (venting is not allowed) before a new refrigerant is added to the system. This is an absolute must to prevent cross-contamination of refrigerants and cooling performance problems.
Mixing different refrigerants can cause big problems. For one, it will increase the system operating pressure. This can result in a loss of cooling performance and may overtax the compressor to the point where it fails. R-134a and mineral oil will not mix. So if somebody recharges an R-12 system with R-134a and does not add a compatible lubricant, the compressor will soon fail.
  • 57% had R-12 and R-134a mixed together (up 10% over last year).
  • 20% had R-22 in R-12 systems.
  • 20% had two or more refrigerants mixed together (down 10% over last year).
  • 30% contained hydrocarbons (propane or other flammable hydrocarbons).
  • 2% had too much air.
The same survey also revealed that only one out of 10 technicians knew about EPA SNAP rules, the Significant New Alternatives Policy regulations that prohibit refrigerant venting, require recovery and recycling, prohibit the intermixing of different refrigerants or the use of flammable refrigerants.
Two out of five technicians also did not know the service fittings on an A/C system MUST be changed if the system is converted from R-12 to R-134a or anything else. And three out of five technicians did not know mixing R-12 and R-134a could cause problems.
For more information about the usage of Alternative Refrigerants, see Alternative Refrigerant Report



Click Here for info about A/C R-134a Retrofit Guide 

 More Air Conditioning Articles:

A/C Cooling Problem: Blows Warm Air Only No Cool Air

Troubleshooting Air Conditioning Problems

Troubleshoot Automatic Climate Control System

Troubleshooting A/C Cooling Problems with Temperature

How To Recharge Your Car's Air Conditioner

Refrigerant Contamination 

Alternative Refrigerants

New Automotive Refrigerants 

Flammable Refrigerants

California proposes ban on R-134a sales to motorists

MACS Recommended A/C Service Procedures (PDF file - requires Adobe Acrobat Reader to view).

A/C Compressor Failures

A/C Condenser Flushing


To More Technical Info Click Here to See More Carley Automotive Technical Articles
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New Automotive Refrigerants

New Automotive Refrigerants For Your Vehicle


alternative refrigerants


What the future holds for automotive refrigerants is uncertain, but changes are happening and more changes are coming. R-134a refrigerant contineus to be used in many late model vehicles, but many new cars are now being equipped with A/C systems that use R-1234yf refrigerant. Other refrigerants may also be coming as R-134 is gradually phased out in the years ahead.
The Europeans want to phase out R-134a in all new vehicles by 2017. The European rules require any new refrigerants must have a global warming potential of less than 150. The U.S. EPA also wants car makers to switch to a different refrigerant to lower the overall carbon emissions of the vehicle fleet. Carbon credits will be given to auto makers who make the switch to a refrigerant that has a lower Global Warming Potential (GWP).
Though R-134a poses no danger to the ozone layer if it escapes into the atmosphere, it is a "greenhouse gas" with a fairly high global warming potential of 1300 (compared to 1 for carbon dioxide, which is nature's own greenhouse gas). A leak that allows only an ounce or two of R-134a to escape into the atmosphere may not seem like a big deal, but over time it all adds up, especially when you multiply small leaks times the hundreds of millions of vehicles that now share planet Earth with humanity.
According to November 2006 report by the Energy Information Administration, vehicles in the U.S. leaked 50.8 thousand tons of R-134a into the atmosphere, equivalent to to over 66 million tons of greenhouse gases. The emissions are 7% higher than in 2004, and up 273 percent since 1995.
North American auto markers have started to replace R-134a with R-1234yf. Auto makers are also redesigning their A/C systems following goals in mind:

* To use less refrigerant. Some newer A/C systems now use only 12 to 14 oz. of refrigerant, which is much less than the 24 to 60 oz. charges that most older A/C systems use. As time goes on, we will see more and more of these low capacity A/C systems in new vehicles.

* To reduce refrigerant leakage 50% over the life of the vehicle. This requires using improved seal designs, hoses and o-ring connections.

* To improve cooling efficiency 30% with more efficient condensers, compressors and operating strategies (things like variable displacement compressors that run all the time rather than cycle on and off). Mercedes has this now.

* To reduce the cooling requirements inside the passenger compartment 30% by using reflective coatings on glass, heat reflective paint, and venting the interior during hot weather.

Changes are also being made to reduce refrigerant losses when the A/C system on a vehicle is serviced. The latest generation of refrigerant recovery machines do a better job of removing all of the refrigerant from the system. Older machines can leave as much as 20 to 30 percent of the old refrigerant charge in the system. The residual refrigerant can escape into the atmosphere when the A/C system is opened to replace parts. Some of the newest machines can pull up to 95% of the refrigerant out of the system to reduce the amount of R-134a that escapes into the atmosphere.

Auto makers have also been adding leak detection dye to the refrigerant to make it easier for technicians to detect refrigerant leaks. A leak will leave a telltale stain that glows greenish-yellow or greenish-blue when illuminated with an UV light source. Leaks as small as 1/8 oz. of refrigerant per year can be detected this way.
The Europeans auto makers are taking a different approach. They want future A/C systems to be as environmentally benign as possible. That means no chlorine-containing CFCs such as R-12 or R-22 that cause ozone depletion, an no refrigerants that could add to the global warming problem (which includes R-134a). Any new refrigerants must also be nontoxic and safe, though that doesn't necessarily mean nonflammable.
For more information, see Flammable Refrigerants
In an effort to address these issues, the Alliance for Responsible Atmospheric Policy (ARAP) and the U.S. Environmental Protection Agency (EPA) have held a series of annual meetings to discuss and evaluate alternatives to R-134a. The first of these meetings was held in 2003 by the European Commission in Brussels. As a result of that meeting, the European Commission decided to allow carbon dioxide, HFC-152a and other refrigerants as possible replacements for R-134a.

CO2 as an Alternative Refrigerant

When used as a refrigerant, CO2 (called R-744) requires extremely high operating pressures (up to 1,800 psi on the high side, and 350 to 400 psi on the low side), compared to 300 to 400 psi on the high side for R-134a. The reason the pressures are so high is because CO2 does not condense in the refrigeration circuit. It remains in the gaseous state. Consequently, the front heat exchanger is called a "cooler" rather than a condenser.
CO2's main attribute is that it has virtually no impact on global warming or ozone depletion. CO2 is also nontoxic in small doses but concentrations over 5% can be lethal. It is also cheap (about $10 for a 20-lb. cylinder) and nonflammable. Numerous test vehicles with CO2 A/C systems have shown that CO2 does provide cooling performance comparable to R-134a.
SAE has developed service fitting standards for R-744. Leak detection presents a challenge because natural levels of CO2 in the atmosphere may be higher than the amount emitted by a leak from an A/C system. Some type of ultrasound or infrared equipment may be required to find R-744 leaks, but dyes may also work or plain old soap bubbles.

HFC-152a

HFC-152a is almost a straight drop-in substitute for R-134a. The molecule is similar to R-134a except that two hydrogen atoms are substituted for two fluorine atoms. It has similar operating characteristics to R-134a but cools even better. One test in an otherwise unmodified Saturn Ion found that A/C duct outlet temperatures were several degrees C lower with HFC-152a. Fuel efficiency was also up 10% at idle, and 20% at highway speeds. The system typically requires only about two-thirds of the normal charge with HFC-152a and can be used with current desiccants.
An environmental benefit of HFC-152a is that it has a global warming rating of 120, which is 10 times less than R-134a, but still a lot higher than CO2. That is why HFC-152a is currently used in many aerosol products as a propellant. Its main drawback is that it is slightly flammable (Class 2A), but it is not as flammable as propane or most other hydrocarbon-based refrigerants.
The first mobile A/C system to use HFC-152a was unveiled at the Mobile Air Conditioning Society (MACS) Worldwide tradeshow in January 2004; a self-contained unit for off-road construction equipment that featured an oil-driven compressor. Made by Red Dot, the unit was a forerunner of future HFC-152a A/C systems to come.
Red Dot staff explained that the HFC-152a refrigerant used in the self-contained unit improves cooling capacity, decreases fuel use and helps protect the climate. The new technology also satisfies stringent new regulations proposed by the European Commission. Red Dot staff also said that the HFC-152a system uses new technology that will use hydraulic-driven compressors and secondary loop technology to increase reliability, safety and reduce the amount of refrigerant required.

R-1234yf

The refrigerant that may eventually replace R-134a is R-1234yf (also called HFO-1234yf). Developed jointly by Honeywell and DuPont, it is being promoted as a drop-in replacement for R-134a in both new vehicles and older vehicles, should that become necessary in the future. R-1234yf has thermal characteristics that are very similar to R-134a, so no major modifications to the A/C system are necessary. Better yet, R-1234yf has a global warming potential of only 4, compared to 1200 for R-134a, allowing it to meet the European requirements for a GWP of less than 150. Existing refrigerant leak detectors can also detect R-1234yf if it leaks. But R-1234yf is mildly flammable (though less so than HFC-152a), and the industry is still debating its potential safety.
Currently, there are NO plans to make R-1234yf directly available to consumers or do-it-yourselfers (meaning you can't recharge your A/C system yourself if your vehicle has an R-1234yf A/C system). Also, repair shops can only buy the new refrigerant in 10-pound containers, limiting the amount they can keep on hand for service work.
In early 2013, production of the new refrigerant began for a limited number of OEM applications. Production has ramped up as more and more new vehicles with R-1234yf A/C systems are introduced.

Click Here for detailed information about R-1234yf by Honeywell.


Update: November 2008

SAE Says HFO-1234yf is Best Alternative Refrigerant for R-134a

In a recent press release, the Society of Automotive Engineers (SAE) International Cooperative Research Program (CRP) says HFO-1234yf offers "superior environmental performance" for future mobile air conditioning systems that may be redesigned for alternative refrigerants.
The CRP1234-1 and CRP1234-2 programs, launched in 2007, have investigated the safety and performance of the new refrigerant HFO-1234yf. Under the direction of the SAE CRP members (who are international experts in this field from OEMs, Tier 1 and 2 Suppliers and independent test facilities), air conditioning system performance, material compatibility and relative risks of HFO-1234yf were evaluated. Based on these studies, HFO-1234yf was judged to have the lowest risk for use in mobile A/C systems compared to all of the other alternative refrigerants that are currently being evaluated. This is based on the Life Cycle Climate Protection analysis that estimates CO2 Equivalent emissions from automotive A/C usage (as described in SAE J2766).
Click Here to view the SAE CRP1234 report on HFO-1234yf.
The study was conducted in response to European Union regulations that will require all new vehicles made for model year 2011 and later to use a refrigerant with a Global Warming Potential (GWP) below 150. Current automotive A/C systems all use R-134a, which has a GWP of 1,430. HFO-1234yf has a GWP of only four.

Update: October 15, 2009

EPA to Approve HFO-1234yf Refrigerant for Significant New Alternatives Policy (SNAP) program

On Tuesday, October 13, 2009, EPA's Administrator signed a rule proposal that says HFO-1234yf is an acceptable substitute for CFC-12 in motor vehicle air conditioning, subject to use conditions. You can view the proposed rule on EPA's SNAP website athttp://www.epa.gov/ozone/snap/.
The public comment period on this proposed rule is for 60 days, beginning when it is published in the Federal Register early next week. Once the rule is published, you will be able to find information and to send EPA comments on the proposed rule athttp://www.regulations.gov/ , docket EPA-HQ-OAR-2008-0664. The Federal Register version of the proposed rule will be posted by the end of the week of October 19 at http://www.epa.gov/ozone/snap/regulations.html (Rule 16 on HFO-1234yf).

Update: September, 2010

GM to Use R-1234yf Refrigerant in some 2013 Models

GM says that starting in 2013, it will begin using HFO-1234yf refrigerant instead of R134a in the air conditioning systems in some Cadillac models (XTS luxury sedan and ATS sports sedan). This will help GM meet the new greenhouse gas emission rules. The Chevy Volt plug-in hybrid electric, however, will have an R134a air conditioning system (for now).

Update: October 21, 2010

SAE Releases 20 New Standards for R-1234yf Refrigerant

The Society of Automotive Engineers (SAE) has announced 20 new standards covering service procedures, service equipment and vehicle components for the new R-12354yf refrigerant. The standards require auto repair shops to buy all new equipment to service the A/C systems on new vehicles that are equipped with HFO-1234yf. The new equipment requirements are covered in J2911, which includes a provision that the recharging machine must test the A/C system for leaks. If a leak is found, the machine will not recharge the vehicle until the leak is fixed. J2843 covers recovery procedures.
J2845 will require technicians who work on R-1234yf systems to be certified in service and recovery procedures.
There is also a new standard J2842 that prohibits shops from repairing leaky evaporators, or fixing a vehicle with a used evaporator from a salvage vehicle because of possible safety risks. R-1234yf is mildly flammable, so the reason for replacing a leaky evaporator with a new one is to minimize the risk of a repeat leak that might allow the refrigerant to enter the passenger compartment.
Currently, there is no mandate in the U.S. to phase-in R-1234yf by a certain date, so the phase in will be gradual and will likely be spread across many model years as new vehicle models are introduced. This will likely create a LOT of confusion in the years ahead as to which type of refrigerant to use in a particular model year vehicle. R134a or other refrigerants must NOT be intermixed with or substituted for R-12354yf in new vehicles if service is required as damage may result to the A/C system due to different operating pressures.
New vehicles with R-1234yf A/C systems also require a unique type of PAG compressor oil. Compressors for these systems have been redesigned to keep more of the oil in the compressor to improve cooling efficiency. Larger, more efficient condensers are also required because R-1234yf cools about 10 percent less efficiently than R134a.

Update: September 4, 2012

MACS Announces R-1234yf Technician Training Program

The Mobile Air Conditioning Society (MACS) now has a new training program to certify automotive technicians to SAE J2845 under the SAE J2911 program for the upcoming introduction of R-1234yf refrigerants in new vehicles.
SAE International created the J2911 and J2845 standards in response to changes in the refrigerants that will be used in mobile A/C systems. The SAE J2845 standard covers servicing of R-1234yf and R-744 mobile air conditioning (MAC) systems. The training teaches technicians how to identify which refrigerant is in a vehicle, how to handle it safely, and what type of service information, tools and equipment are needed to service the vehicle.

Update: November 2012

Mercedes, BMW and VW say they will NOT use R-1234yf Refrigerant because of Safety Concerns

Citing concerns that the alternative refrigerant R-1234yf can burn in real life conditions inside a vehicle (per lab simulation test results), Mercedes, BMW and Volkswagen said they will NOT switch their vehicles to R-1234yf. At this time, it appears that CO2 may be the best alternative to R-134a, according to the German auto makers.
R-1234yf can by ignited by a spark within seconds of its release, and emits highly toxic fumes and acids as it burns according to tests conducted by Daimler. CO2 is nonflammable and is carbon neutral, so it appears for now that R-1234yf is on hold as far as two of the leading German auto makers are concerned.
On a related note, Cadillac has temporarily suspended installing R-1234yf in the ATS sports sedan and XTS luxury sedan. For now, these vehicles will be produced with R-134a pending further investigation into the potential flammability issues with R-1234yf.
Note: See June 26, 2013 update below for more information on this subject.

Update: April 13, 2013

Latest Alternative Refrigerant May be a Blend Called AC-6

To counter the virtual monopoly that Honeywell and DuPont have on the production of R-1234yf refrigerant (which is currently selling to car dealers for around $60 to $70 a pound!), Mexichem has developed a blended refrigerant that could sell for as little as $10 a pound, and would work in any R-134a A/C system. The AC-6 blend contains 85 percent R-1234ze, 9 percent R-134a and 6 percent CO2. The Global Warming Potential (GWP) of the new blend is 6.0, which is well under the GPW requirement of 150.
For AC-6 to be approved, the auto makers would have to do extensive testing, and the EPA would have to add it to its approved alternative refrigerant list.
The main drawback of a blended refrigerant is that some of the ingredients in the mix tend to leak out of an A/C system faster than others, effectively changing the blend over time and its thermal characteristics. Currently, there is no aftermarket A/C service equipment that can reconstitute a blended refrigerant. If an A/C system charged with AC-6 required service, the old refrigerant would have to be recovered from the system and replaced with new refrigerant rather than recycled.

Update: June 26, 2013

SAE now says R-1234yf is Safe for Use in Passenger Car A/C Systems

After extensive testing and review, SAE International has concluded that Honeywell's new R-1234yf low-global-warming-potential mobile air conditioning refrigerant is safe for use in automobiles. Yes, it can be flammable under certain conditions, but those conditions are highly unlikely to occur in a real world crash, concludes SAE.
To read the official press release, Click Here.

Update: April 2014

R-1234yf A/C Systems Now in Production

The first U.S. vehicle to use R-1234yf refrigerant was the 2013 Cadillac XTS. Cadillac also tried R-1234yf in the Cadillac ATS, but stopped only one month into production because of A/C compressor noise and vibration issues. Early production ATS models were recalled and retrofitted back to R-134a (which apparently works fine in an A/C system designed for R-1234yf).
For model year 2014, R-1234yf is used in the Jeep Cherokee, Chrysler 300, Dodge Ram 1500, and Dodge Charger, Challenger and Dart. It will also be used in the 2015 Chrysler 200.
Most auto makers are expected to have numerous R-1234yf applications by model year 2017 and beyond. Auto makers receive fuel economy credits for vehicles that are converted to R-1234yf, which helps them achieve the new higher Corporate Average Fuel Economy (CAFE) requirements.



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Flammable Refrigerants

Flammable Refrigerants To Be Taken Care Of 


flammable refrigerant caused car fire


Flammable refrigerants are illegal to use in an automotive air conditioning system. There are some exceptions, such as the new R1234yf refrigerant, which is mildly flammable but only under certain conditions. Flammable refrigerants may also be used in the trailer refrigeration units on heavy duty trucks. But other than these, no flammable refrigerant should ever be used in a car or light truck A/C system.

Flammable Refrigerant Fire Hazards

Propane, butane and a number of other hydrocarbon mixtures and blends actually work quite well as refrigerants, with cooling characteristics similar to R-12, R-22 and R-134a. But if the evaporator inside the passenger compartment develops a leak, the flammable vapor may create a potential for a fire or explosion. Do you really want to risk being cremated while driving your vehicle?
Another thought to keep in mind is what happens if your vehicle is involved in an accident. The A/C condenser sits right in front of the radiator and contains high pressure refrigerant vapor and liquid. If the condenser is ruptured in a frontal collision (which it often is), high pressure flammable vapor will be released, almost guaranteeing an underhood fire!
Do you really want to risk your life or the lives of your passengers by using a cheap flammable refrigerant in your vehicle's air conditioning system? R-134a is the only refrigerant that should be used when recharging a late model automotive A/C system.

EPA SNAP Rules on Flammable Refrigerants

The US EPA SNAP regulations do NOT allow the use of flammable refrigerants in vehicles.
The only exception is a new refrigerant called HFO-1234yf which is only mildly flammable under certain conditions. For info on EPA SNAP regulations, see this link:
The Mobile Air Conditioning Society (MACS) also does NOT approve of using flammable refrigerants. Nor does the Society of Automotive Engineers (SAE). Like the EPA SNAP rules, the only exception is the new HFO-1234yf refrigerant that will start appearing in some new cars in 2013 or beyond as a replacement for R-134a.

Use R-134a Only

The EPA, MACS and SAE all say that the only acceptable replacement refrigerant for newer R-134a system is R-134a. Nothing else should be used to avoid cross-contamination problems and cooling performance issues. Older vehicles with R-12 can be retrofitted with R-134a or other approved alternative refrigerants (which also must NOT be flammable).
Here is document that contains a lot of good information about alternative refrigerants, though it is dated 1999. The basic information is unchanged, and the only update would be the approval of HFO-1234YF for future A/C systems.
Flammable Refrigerants are Against the Law!
Many city municipalities and states have laws prohibiting the use of flammable refrigerants in vehicles.
In Europe, propane is allowed in some home refrigerators, but the amount is so small that it poses no explosion or fire hazard. Refrigerators must also pass safety tests that show any refrigerant leak cannot create a fire or explosion hazard.

Flammable Refrigerants: OZ-12 and HC-12A

Alternative refrigerants that do not meet the EPA's criteria for environmental acceptability or safety include OZ-12, HC-12a, R-176 and R-405a. Flammable refrigerants such as OZ-12 and HC-12a contain large quantities of hydrocarbons (propane, butane, isobutane, etc.) and have been declared illegal for use in mobile A/C applications but are still finding their way into A/C systems because of their cheap price.
The EPA does not approve of flammable refrigerants because the EPA says they pose a significant danger to a vehicle's occupants should a leak occur. The EPA says a spark from a cigarette or a switch could ignite leaking refrigerant causing an explosion and fire.
Counterpoint: The makers of HC-12a contend that the flammability danger is highly exaggerated and there is "no evidence" to support claims that a cigarette or spark can ignite their product. They also contend that the EPA's position on their product is unfair, and that HC-12a has been successfully used in many vehicle A/C systems worldwide with no accidents or injuries due to ignition.

HFC-152a

Another alternative refrigerant that has been proposed for automotive use is HFC-152a. It has a GWP rating of 140, which meets the European requirements for combating global warming. HFC-152a has cooling characteristics very close to that of R-134a, and could probably be used as a direct substitute for R-134a with few if any modifications. But HFC-152a is flammable, so it is currently illegal to use.
One possible solution to the flammability issue HFC-152a (or other flammable refrigerants) is to add a leak sensor inside the vehicle that warns the passengers if a leak occurs, and automatically opens the power windows to vent the vapors (thus, reducing the fire/explosion risk).
Another solution is to redesign the A/C system so that it uses a "secondary loop" to keep the flammable refrigerant in the engine compartment and out of the passenger compartment. With this approach, the refrigerant circulates through an intermediate heat exchanger and chills a liquid (probably a water/antifreeze mixture) that then flows through the HVAC unit inside the vehicle. A recent report from the U.S. EPA says this approach meets its safety criteria, while also being energy efficient. But it does not reduce the risk of fire in a frontal collision, and it still poses a risk to technicians and do-it-yourselfers while recharging or servicing the A/C system.

HFO-1234YF

The newest alternative refrigerant is HFO-1234yf. The refrigerant replaced R-134a in model year 2014 on a few vehicles. It has thermal characteristics that are similar to R-134a, so only minor modifications to the A/C system are necessary (larger condenser and different PAG oil). It has a low GWP rating of only 4, which meets the European requirements for reducing global warming. But it is mildly flammable (though much less so than HFC-152a) and will only burn under certain conditions which should NOT occur in normal automotive usage.
For more information about HFO-1234YF, see 1234facts.com.

Update: November 2012

Volkswagen says it will NOT use HFO-1234yf Refrigerant because of Safety Concerns

Citing concerns that the alternative refrigerant HFO-1234yf can burn in real life conditions inside a vehicle, Volkswagen said that it will NOT switch its vehicles to HFO-1234yf. At this time, it appears that CO2 is the best alternative to R-134a, according to VW. This decision follows a similar announcement late last month by Daimler (Mercedes Benz) to abandon work on HFO-1234yf in favor of CO2 or other alternative refrigerants.
HFO-1234yf can by ignited by a spark within seconds of its release, and emits highly toxic fumes and acids as it burns according to tests conducted by Daimler. CO2 is nonflammable and is carbon neutral, so it appears for now that HFO-1234yf is on hold as far as two of the leading German auto makers are concerned.

Update: June 26, 2013

SAE says HFO-1234yf is Safe for Use in Passenger Car A/C Systems

After extensive testing and review, SAE International has concluded that Honeywell's new HFO-1234yf low-global-warming-potential mobile air conditioning refrigerant is safe for use in automobiles. Yes, it can be flammable under certain conditions, but those conditions are highly unlikely to occur in a real world crash, concludes SAE.
To read the official press release, Click Here.



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