HFC - R134a

Application Temperature Range
R-134a performance suffers at lower evaporator temperatures. In general it is not applied at temperatures below -10F, and it is not necessarily the most economical overall choice in some other applications. Traditional R-12 type applications have adopted several products as alternatives, including R-134a, R-22, R-404A/R-507, and numerousretrofit blends.

Lubrication
R-134a requires polyol ester (POE) lubricants, primarily for their ability to mix with HFC refrigerants. Traditional mineral oils and alkylbenzene do not mix with HFCs and will
cause compressor failures. In addition, automotive air conditioning systems may also use polyalkaline glycol (PAG) lubricants (not typically seen in stationary equipment). Both POEs and PAGs will absorb moisture, and hold onto it, to a much greater extent than traditional lubricants. The moisture will promote reactions in the lubricant as well as the usual problems associated with water (corrosion, acid formation, etc.). The best way to dry a wet HFC system is to use a filter drier - run the system and change the drier - instead of relying on evacuation to clear the water.

Retrofitting Considerations
Equipment built for R-12 will be sized a bit too small compared to equipment built for R-134a. In order to do the same job an R-134a system will need a larger compressor and larger heat exchangers. As a result a system which is retrofit from R-12 to R-134a will have lower capacity (run longer) and will probably develop higher head pressures (not enough condenser area). The lubricant will also need to be flushed and replaced with POE (residual mineral oil content less than 5%).