By Robert Pontiff

Most of you are aware that the refrigerant used in automobiles has changed. The standard refrigerant for the past 40 or so years has been a chlorofluorocarbon known as FREON-12 (trade name for R-12 or CFC-12). Scientists have determined that chlorofluorocarbons deplete the ozone layer. This article will not debate the merits of the scientific conclusion, but instead will focus on the impact to the old car hobby.

The horror story of high cost conversions to lower efficiency systems has caused many people to panic. I am sure that you can find stockpiles of FREON-12 in garages all over the country. But fear not, the dog's bark is much worse than his bite.

The Environmental Protection Agency (EPA) has approved and rejected a number of alternative refrigerants. EPA approval only attests to the fact that the refrigerant does not deplete the ozone and that it is nonflammable and non-toxic. The EPA does not verify performance or compatibility to existing systems.

Original Equipment Manufacturers (OEM) have selected refrigerant "R-134a" as the new refrigerant to be used in cars, but others are available. Many companies advertise "drop-in" replacements. The definition of drop-in is not clear. Mixing of refrigerants in a system is against the law, and the affects of mixing FREON and other refrigerants are not widely known. One definition of "drop-in" could be that the replacement of the FREON would require little or no hardware change. "R-134a" may meet this definition for "drop-in". "R-134a" has been selected as the industry standard and its availability in the foreseeable future is assured. The focus of this article will be the modification of an automobile system to use "R- I 34a" because of the above reasons.

The following steps for replacement are based on the assumption that your system provides acceptable cooling for your climate and that it is not a "leaker".

1) The first step is to recover the R-12 from your system. You may require a professional because of the equipment required. You should not "vent" the FREON to atmosphere for at least two reasons: 1) FREON venting may be detrimental to our world and 2) the recovered FREON can be reused and, therefore, extent the availability for systems that cannot be converted. If the system has been opened or contaminated, a closed-loop flush is in order.

2) Once the R-12 has been removed from the system it is time to address hardware changes:

Hoses: "R-134a" molecules are smaller than R-12 molecules. Because of this, it was felt that new hoses called "barrier hoses" were required. This has turned out to be an unwarranted concern. Recent tests have shown that oil used in the air conditioner system is absorbed into the hoses to create a natural barrier to "R-134a" leakage. It should be noted that other "drop-in" replacements may contain HCFC-22 which mandates installation of "barrier hoses" to preclude leakage.

Compressor, evaporator, expansion valve, orifice tube, o-rings and/or seals: They do not require replacement in general unless they are leakers or damaged. Some compressors use Viton seals that swell excessively when in contact with "R-134a". It may be appropriate but not mandatory to change all Viton seals. R-12 causes a thin film of metal chloride to form on compressor bearing surfaces. This metal chloride is an excellent wear agent that will continue to protect and increase the life of the compressor even after it is converted to "R-134a". This suggests that it may be better to re-use your old compressor versus using a new R- 12 compressor.

Desiccants, accumulators or receiver/dryers: Older cars will require replacement with a part that contains a desiccant that is compatible with "R-134a". This is a relatively low dollar item. Many air conditioner experts recommend changing the dryer after a system has been opened anyway.

Condensers: In most cases, replacement is not required. Higher vapor pressures could result in loss of condenser capacity, thus decreasing the effectiveness of the air conditioner. Most automotive air conditioners are sufficiently over-designed and the small loss of effectiveness would not be noticed. If excessive high-side pressure is noted at idle or if the A/C does not cool well, the solution could be to add a "pusher-type" electric radiator fan as opposed to condenser replacement. The condenser should also be inspected to assure that the fins are not bend or blocked. Air flow dams, radiator shroud and a fully functional fan clutch are also important considerations in maintaining adequate air-flow over the condenser.

Pressure limiters: "R-134a" systems generally function at 10-15% higher pressure than R-12 systems. It may be appropriate to install a pressure-limiter switch. If your A/C has a clutch cycling orifice tube system, then the cycling switch should be adjusted.

3) Oil should be flushed from the system and drained from the compressor. The mineral oil used for R-12 systems is too heavy to be transported through the A/C system by "R-134a". A PAG or an ester lubricant should be used in its place. Both these lubricants tend to absorb moisture (hygroscopic) but esters to a lesser degree. Use only PAGs and esters from a tightly sealed container.

4) Replace R-12 service ports and labels with ones specified for "R-134a". It is important to install the retrofit label and new service ports to assure proper recharging in the future.

5) Charge the system with "R-134a". It generally takes 10 to 20% less "R-134a" that R-12 to fully charge the system.