Guidance on Retrofitting to HFC-134a
The term "retrofit" describes special procedures required to convert an R-12 system to use an alternative refrigerant. This document will describe some facts about aftermarket options and procedures for retrofitting a vehicle's air conditioning system to R-134a.
Automakers worldwide chose R-134a to be the long-term replacement for R-12 in automotive a/c systems, both in new vehicles and in retrofit applications. If information becomes available, EPA may develop similar guidance in the future for retrofitting to refrigerants other than R-134a. At this time, however, wide-scale performance testing has not been performed on vehicles retrofitted to other refrigerants. Should you have questions about retrofitting to an alternative refrigerant, consult the refrigerant's manufacturer as well as the manufacturer of your vehicle. You may also want to review the EPA publication Choosing and Using Alternative Refrigerants in Motor Vehicle Air Conditioning.
Table of Contents
- OEM Retrofits
- Least-Cost Aftermarket Retrofit
- Communicating With the Customer
- EPA Requirements for Retrofit
- A Word on Replacements Other Than R-134a
- R-134a Refrigerant
- Hoses and O-Rings
- Desiccants, Accumulators, Receiver/Driers
- Condensers and Pressure Cutout Switches
- Refrigerant Controls
In addition, because the OEM retrofit kits and guidelines are generally only available for late 1980s and early 1990s models, an aftermarket retrofit may be the only option for many vehicle owners.
Many car owners may express interest in receiving a least-cost retrofit. Procedures required for a least-cost retrofit are simple and do not require major component changes. Generally, the process calls for removal of the old refrigerant, installation of new fittings and a new label, and the addition of either a polyalkylene glycol (PAG) or polyol ester (POE or ester) lubricant as well as the R-134a refrigerant. For many vehicles, this simple, least-cost retrofit should provide the vehicle owner either with a/c performance comparable to the R-12 system performance or with a/c performance that, although slightly reduced, is still sufficient to satisfy the customer. A least-cost retrofit, however, may not provide a satisfactory solution for certain vehicles.
Although EPA has been educating car owners about options available to them in converting their a/c systems, many consumers will rely primarily on their service technician to educate them. Service facilities that wish to offer retrofit as a service to their customers need to consider what kind of retrofit procedure they will offer, and how they will warranty the work performed. When determining whether to recommend a retrofit to a customer, and what kind of retrofit to offer -- an OEM-warrantied retrofit (if available), a least-cost retrofit, or something in between -- a service tech will need to consider (or ideally, discuss with the customer), the three C's: cost, climate and components.
- How much is the customer willing to spend? How much longer will he or she own the vehicle? Is the vehicle a refrigerant leaker or is this the first time in the life of the vehicle that the a/c system has been serviced?
- Does the customer need minimal a/c performance (because s/he only takes the car out on Sundays in mild conditions), or extreme a/c performance (because s/he uses the car six days a week in hot conditions)? If the latter, is s/he so concerned about retrofit cost that s/he would prefer the least-cost retrofit, even if that retrofit will not, in the technician's judgment, provide performance comparable to the system performance with R-12?
- Are the existing components in the a/c system in good shape? Are they compatible with R-134a?
If an R-12 system is performing marginally, retrofitting alone will not make it better. In fact, since R-12 systems were not designed for use with R-134a, owners should be prepared for a slight reduction in a/c performance. In most parts of the country, this reduction will not be significant, and vehicle owners may not notice any difference in performance.
In warmer climates, however, where the a/c system is running at full blast many months during the year, performing a simple, least-cost retrofit may not produce satisfactory performance. In that case, a technician should be able to recommend what additional steps are most appropriate -- possibly installing a larger condenser, or adding a fan or high-pressure cut-off switch. Although these steps make the retrofit more expensive, at least the car owner has a choice of options.
In addition, on older models, it may be necessary to replace worn a/c system components. R-134a may operate at higher pressures than R-12, and these higher pressures may put additional stress on the a/c system, so that older, worn components may be more likely to fail.
Some vehicles may also have components that were not specifically designed with R-134a in mind, and as a result may not withstand the higher pressures of R-134a. As a result, these components may experience a shortened service life. That service life may be shortened only slightly, or a great deal. Only wide-scale durability testing on thousands, if not millions, of retrofitted vehicles will provide the automotive service industry with a full understanding of how retrofit affects the life of each a/c system component.
Service techs should keep in mind that there is no such thing as a universal retrofit procedure, or a simple kit a technician can purchase that will provide all the necessary parts to guarantee a successful retrofit for every make and model. Even within particular models, retrofit requirements may vary. A particular make, model and year vehicle driven for 90,000 miles in Houston may require a more extensive retrofit than the same make, model and year driven for 35,000 miles in Minneapolis.
The Society of Automotive Engineers (SAE) provides guidelines for a/c retrofit in their publication J1661. Several refrigerant and lubricant producers have published their own recommendations. EPA is compiling a list of organizations that offer either classroom or home-study (videotape/workbook) retrofit training. For EPA's current list, see "Training on Retrofitting to R- 134a."
According to EPA regulations, the use of any alternative refrigerant to replace R-12 requires at a minimum that:
- unique service fittings be used in order to minimize the risk of cross-contamination of either the air- conditioning system or the service facility's recycling equipment;
- the new refrigerant be identified by a uniquely-colored label in order to identify the refrigerant in the system;
- all R-12 be properly removed from the system before filling the system with an alternative refrigerant;
- in order to prevent release of refrigerant to the atmosphere, a high-pressure compressor shutoff switch be installed on any system equipped with a pressure relief device; and
- separate, dedicated EPA-approved equipment be used to recover the R-12 from the system.
- In addition, alternative refrigerant blends that contain HCFC-22 must be used with barrier hoses.
A number of refrigerants other than R-134a have been listed by EPA as acceptable under its Significant New Alternatives Policy (SNAP) program, or are under SNAP review. The SNAP program evaluates substitutes only for their effect on human health and the environment, and not for performance or durability. None of these refrigerants have been endorsed by the OEMs for use in vehicles, and few have had extensive testing in a wide range of vehicle models. In addition, most are currently not readily available in all areas of the country.
While some manufacturers of alternatives may be marketing their products as "drop-ins," keep in mind that because the regulations described above apply to any substitute for R-12, there is no such thing as a refrigerant that can literally be dropped in on top of the existing R-12 in the system. For more information on the SNAP requirements and on which alternatives have been reviewed, accepted, or deemed unacceptable by EPA, see the fact sheet "Choosing and Using Alternative Refrigerants in Motor Vehicle Air Conditioning."
Many service techs believe that R-134a is only a temporary replacement for R-12, to be used until a drop-in replacement that cools well and does not require a retrofit becomes available. Current research indicates that no such replacement refrigerant exists. The worldwide automotive industry conducted extensive research and testing on many potential substitutes for R-12 before selecting R-134a. EPA is not aware of any plans by the automakers to use any refrigerant in new vehicles other than R-134a.
Toxicity, Flammability, Corrosion
R-134a is regarded as one of the safest refrigerants yet introduced, based on current toxicity data. The chemical industry's Program for Alternative Fluorocarbon Toxicity Testing (PAFTT) tested R-134a in a full battery of laboratory animal toxicity studies. The results indicate that R-134a does not pose cancer or birth defects hazard. In addition, R-134a is being used in metered dose inhalers in Europe.
OEM engineers and chemical manufacturers have examined the flammability and corrosivity of each potential R-12 substitute. Like CFC-12, R-134a is not flammable at ambient temperatures and atmospheric pressures. However, R-134a service equipment and vehicle a/c systems should not be pressure tested or leak tested with compressed air. Some mixtures of air and R-134a have been shown to be combustible at elevated pressures. These mixtures may be potentially dangerous, causing injury or property damage. R-134a is not corrosive on standard steel, aluminum and copper samples.
When handling R-134a, as with any other chemical, service techs should be sure to work in a well ventilated area. It is never a good idea to inhale any vapor to such an extent that it replaces the oxygen in your lungs.
How Much to Charge into the System
The amount of R-134a charged into the system should normally be 80-90% of the amount of R-12 in the system. Most a/c system manufacturers provide guidelines regarding the amount of R-134a to be used.
PAGs vs. Esters
The mineral oil used with R-12 cannot be sufficiently transported throughout the a/c system by R-134a. Automobile manufacturers tested both PAGs and esters for refrigerant/lubricant miscibility, lubricity, chemical stability and materials compatibility. In the process of developing recommendations, they also considered the additives and conditioners present in the oils. Most - but not all - chose to use PAG lubricants in new vehicles equipped with R-134a, and are also recommending PAG lubricants for retrofits. Some compressor manufacturers are shipping new compressors with PAGs, some with esters, and some are shipping them empty.
PAGs are hygroscopic, which means that they will draw water from the atmosphere when exposed. Many aftermarket a/c specialists are choosing to use ester lubricants because they believe that the hygroscopic characteristics of PAGs may limit their lubricating ability and introduce corrosion into an a/c system. Esters are also hygroscopic (although less so than PAGs), and care must still be taken to ensure that excess moisture does not go into the system.
It is good practice to use PVC-coated gloves (or, if that is impractical, barrier creams) and safety goggles when handling these lubricants, since prolonged skin contact and/or even brief eye contact can cause irritations such as stinging and burning sensations. You should also avoid breathing any vapors produced by the lubricants, and make sure to use them in well ventilated areas. And be sure to keep both PAGs and esters in tightly sealed containers, both so that humidity does not contaminate the oil, and so that vapors do not escape.
The amount of mineral oil that can safely remain in a system after retrofitting, without affecting performance, is still being debated. It was originally thought that any mineral oil left in the system might cause system failure. As long as the tech has removed as much of the old mineral oil as possible, any residual R-12 left in the system should not have a significant effect on the performance of the system. Removing the mineral oil may require draining certain components. Unless the vehicle manufacturer recommends flushing the system during the retrofit procedure, a service tech can assume that flushing is not necessary. (Although the SAE J1661 procedure for retrofit includes flushing, SAE no longer believes that flushing is critical to a successful retrofit.)
When R-134a was first introduced, it was thought that all non-barrier/nitrile hoses would have to be replaced during an a/c retrofit. Early laboratory tests showed that the small R-134a molecules leaked through the walls of non-barrier hoses more readily than the larger R-12 molecules did. In the lab, this caused unacceptably high leakage rates. More recent testing, however, has shown that oil used in automotive a/c systems is absorbed into the hose to create a natural barrier to R-134a permeation. In most cases, the R-12 system hoses will perform well, provided they are in good condition. Cracked or damaged hoses should always be replaced with barrier hoses.
Unless a fitting has been disturbed during the retrofit process, replacement should not be necessary. Most retrofit instructions call for lubricating replaced O-rings with mineral oil to provide this protection.
Industry experts once thought that a retrofit would require compressor replacement. This belief helped create some of the horror stories about the expense of retrofitting. Now it is routinely accepted that most compressors that are functioning well in R-12 systems will continue to function after the systems have been retrofitted.
When a compressor is first run with R-12, a thin film of metal chloride forms on bearing surfaces and acts as an excellent anti-wear agent. This film continues to protect after the system has been converted to R-134a. This helps explain why a new R-12 compressor may fail more quickly if it is installed in an R-134a system without the benefit of a break-in period on R-12.
A few older compressors use seals that are not compatible with either R-134a or the new lubricants. The compressor manufacturer can identify which compressors need special attention. Any compressor that has seals made of Viton® should not be used with R-134a because the refrigerant will cause the seals to swell excessively.
Of course, any compressor that is not in good shape should be replaced during the retrofit procedure. Service techs should make sure that any replacement compressor is approved for R-134a by its supplier.
R-12 systems use an XH-5 desiccant, while R-134a systems use either XH-7 or XH-9 desiccant. Some manufacturers recommend routine replacement of the accumulator or receiver-drier to one containing XH-7 or XH-9 during the retrofit procedure. (Any systems with silica gel should also be switched to XH-7 or -9 desiccant.) Others recommend leaving it alone. Manufacturers generally agree, however, that the accumulator or receiver-drier should be replaced if the vehicle has over 70,000 miles or is older than five years, and is opened up for major repair. In that case, the only recommendation is to use the R-134a-compatible desiccants.
When retrofits were first studied several years ago, it was thought that the condenser and perhaps the evaporator would have to be replaced to maintain an acceptable level of cooling performance on a retro-fitted system. Now, it is generally accepted that if an R-12 system is operating within the manufacturer's specifications, there may be no need to replace either part.
It is true, however, that the higher vapor pressures associated with R-134a may result in lost condenser capacity. When retrofitting, service techs should consider how the air flow and condenser design on the particular vehicle will affect the success of the retrofit. In some cases, the installation of pusher-type engine/condenser cooling fans mounted in front of the condenser have improved the performance of retrofitted a/c systems.
Service techs should also be aware that bent, misshapen or improperly positioned airflow dams and directors may affect performance. Some OEMs are including hood seal kits as part of their recommended retrofit procedures. In addition, systems that are not equipped with a high-pressure cutout switch should have one installed to prevent damage to a/c parts and to prevent refrigerant emissions. The installation of a high-pressure cutout switch will shut off the compressor when high pressures are encountered, reducing the possibility of venting the refrigerant and overheating the engine cooling system.
Refrigerant controls -- whether they are orifice tubes or expansion valves that meter refrigerant flow, or pressure cycling switches or other pressure controls designed to protect against freezing -- may have to be changed during the course of a retrofit.
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