Automotive Air Conditioners
Factory R-134a systems are generally equipped with barrier style hoses to reduce seepage that can lead to refrigerant loss over time. It may not be necessary to replace the hoses when converting an R-12 system with non-barrier hoses to R-134a as long as the hoses are in good condition. This is because the hoses have absorbed oil that forms a barrier of its own. But if the old hoses are leaking, they should be replaced with new barrier style hoses.
O-rings on some applications may also have to be replaced with materials such as HNBR or Neoprene W that are compatible with R-134a. On some applications, the conversion process isn't so easy because the compressor seals are Viton that is incompatible with R-134a. Some OEM compressors are also not rugged enough to withstand the higher operating pressures of R-134a. Consequently, converting one of these systems requires a new compressor, which would not be cost-justified unless the compressor had failed and needed replacing anyway.
Factory R-12 systems generally use mineral oil while R-134a systems use various types of PAG (polyalkylene glycol) oil because mineral oil does not mix with R-134a and PAG oil does not mix with R-12. Some conversions also require replacing the high-pressure cutoff switch and/or orifice tube or expansion valve with ones calibrated for R-134a.
It's important to note that the conversion process is not something for do-it-yourselfers. It's for professional technicians who have obtained an EPA-approved certification in R-12 recovery and recycling procedures and have the required service equipment to make the necessary changes.
The demand for R-134a conversions will grow as the remaining supplies of virgin and recycled R-12 disappear. As long as R-12 is still available, there's no reason not to continue using it because R-12 poses no environmental threat as long as it remains inside a vehicle's A/C system. A/C systems designed to operate with R-12 refrigerant cool best with R-12. Converting to R-134a may also reduce cooling performance
The reason vehicle manufacturers choose R-134a to replace R-12 is because R-134a comes closer to the cooling properties of R-12 than any other alternate refrigerant. Even R-134a is so close to R-12; it is not a direct replacement. They are chemically different and incompatible because each requires a different type of compressor oil and desiccant. Since they are different, federal law prohibits mixing the two to prevent cross contamination. It is also federal law that shops doing A/C work are required to recover and recycle R-12 whenever they perform any repairs to an R-12 system.
Even though they are different, R-134a can be used in an R-12 system provided the system is converted or "retrofitted" to the new refrigerant. The way this is done will vary from one vehicle to another, but in most cases it will require:
- Removing and recovering all the old R-12 refrigerant from the system.
- Changing the desiccant (accumulator or receiver/drier) to one that is compatible with R-134a.
- Adding compressor oil that is compatible with R-134a (PAG or POE oil)
- Installing R-134a fittings (which are different from the threaded fittings on R-12 systems.
- Recharging with system to about 80 percent capacity with R-134a refrigerant.
- Labeling the system to identify it has been converted to R-134a.
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