Back when HFC-134a was the only acceptable replacement refrigerant for CFC-12, many in the industry were concerned about the potential for cross-contamination, or mixing, of the two refrigerants in motor vehicle air conditioning (MVAC) applications. The proliferation of Environmental Protection Agency (EPA) acceptable alternatives to CFC-12 has escalated this potential into what some consider to be a significant problem. While unique, refrigerant-specific fittings, labels and service equipment (required by the EPA) were developed and implemented to prevent cross-contamination, these measures have not been completely effective. The incidence of two or more different refrigerants in an A/C system has become increasingly more frequent. The most recent IMACA retrofit survey shows that, compared to the two preceding years, contamination rates doubled from 1996 to 1997, and doubled again from 1997 to 1998.

Mixed refrigerants present several costly dangers for the service facility. First, they cannot be separated with the existing MVAC recover/recycle equipment, and therefore, contaminate both the equipment and the supply of refrigerant already in the recovery cylinder. Second, once the contaminated refrigerant has been recovered into a cylinder, it can find its way into other vehicles brought in for service, spreading contamination like a virus. And third are the obvious hazards from a system containing a hydrocarbon - a flammable substance installed as a refrigerant.

In addition, mixed refrigerants:

• Can produce high discharge pressures.
• Can create various pressure/temperature relationships within the system, depending on the mixture's composition.
• Can be difficult or impossible to identify on-site at the service facility.
• Can not be separated by an on-site recycling machine.
• May trigger the recycling machine's automatic purge vent.

Cross-contamination can be prevented by first accurately identifying the refrigerant in the MVAC system and then servicing only those vehicles whose refrigerant is compatible with your service equipment. Unfortunately, refrigerant identification is not all that simple.

Here are a few suggestions:

1. First, ask the customer about the service history of the A/C system. Although the information may not always be accurate, customer response may help you decide whether to accept or refuse the job.
2. Visually inspect the A/C system. Is the original OEM label present? Is there a retrofit label that has been completely filled out? Are the service port fittings correct for the refrigerant stated on the label?
3. Use a refrigerant identifier/analyzer to determine the purity of the refrigerant remaining in the system.

Today's electronic refrigerant identifiers range from those that can identify contaminated refrigerant but not the specific contaminant, up to units that can accurately identify percentages of specific refrigerant, NCGs (air) and flammable hydrocarbons. Even if the refrigerant is contaminated or unidentifiable, it must be recovered from the MVAC system prior to service - EPA regulations prohibit venting of any refrigerant. A recommended practice is to dedicate a recover-only unit to anything that is not pure CFC-12 or pure HFC-134a. The questionable (junk) refrigerant is recovered into a standard DOT-certified cylinder that has been painted gray with a yellow top and labeled as "contaminated refrigerant." When full, the cylinder can be sent to a reclaimer for processing or disposal.

NOTE: If the cylinder is not equipped with a float valve (which serves as overfill protection), it should not be filled beyond 60 percent of its gross weighted capacity, and be stored in a cool place away from direct sunlight.

Cross-contamination will not resolve itself - not through attrition, or through increased education. We can, however, elect not to become a part of the cycle. We can choose to do the job by the book every time we step into the service bay. We can learn to "just say no" when a questionable vehicle pulls into the service bay.

Frank Allison is the executive director of the International Mobile Air Conditioning Association (IMACA).

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