If you drive an older vehicle (pre-1994), the air conditioning system contains R12 refrigerant (Freon). As long as the A/C system has no leaks and it cooling normally, there is no need to convert from R12 to the new "ozone safe" R134a 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 R12 to R134a when you recharge the system
Why? Because R12 is no longer produced in the U.S. Supplies of recycled R12 still exist, and some R12 is still brought in from offshore suppliers. But it is hard to find and expensive. That's why many people simply recharge their older R12 air conditioning system with R134a after repairs have been made.
Does it make economic sense to retrofit an older vehicle to R134a 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.
WHAT TO USE
There is NO reason to retrofit a vehicle to R134a as long as the R12 system is cooling properly and contains a normal charge of refrigerant. A/C systems designed to use R12 will cool best when charged with R12 refrigerant. Even if the system leaks, repairing the leaks and recharging it with R12 is usually the best repair alternative. Converting to R134a 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 R134a 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 R134a, the only thing that has to be changed is the compressor lubricant.
TWO WAYS TO DO A 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 R134a. 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 R134a.
Federal law also requires the permanent installation of R134a 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 R134a.
The other approach to retrofit is the "quick and cheap" one. On many 1989 through 1993 vintage vehicles, R12 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 R134a.
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 R134a raises compressor discharge pressures and increases the compressors work load, some lightweight compressors may not be rugged enough to tolerate R134a 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 R12 system is converted to R134a. Systems with relatively large or efficient condensers will experience less of a drop in cooling performance with R134a than those with smaller or less efficient condensers.
One way to improve cooling performance when retrofitting an older R12 system to R134a 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 R134a. 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 R134a. 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.
The vehicle manufacturers still do not approve of any alternative refrigerants other than R134a 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 R12 in older vehicles.
It is important to remember that R134a or any other alternative refrigerant cannot be mixed with R12 or used to top off an R12 system. If an A/C system still contains any R12 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. R134a and mineral oil will not mix. So if somebody recharges an R12 system with R134a and does not add a compatible lubricant, the compressor will soon fail.
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 R12 to R134a or anything else. And three out of five technicians did not know mixing R12 and R134a could cause problems.
For more information about the usage of Alternative Refrigerants, see Alternative Refrigerant Report