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.
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
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.
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%).