Key Adjustments for Refrigeration Systems When Replacing R12 with R134a

The thermodynamic properties of R134a are similar to those of R12, but their physical properties differ. Therefore, corresponding adjustments to the refrigeration system are required when using R134a as a substitute for R12. In terms of differences in physical properties, R134a is immiscible with mineral oil, while R12 has good miscibility with it. This means that the mineral oil in the original system must be replaced with polyol ester (POE) oil or polyalkylene glycol (PAG) oil which are compatible with R134a. Failure to do so will prevent the lubricating oil from circulating with the refrigerant, leading to insufficient lubrication of the compressor, which in turn causes compressor wear and even burnout. Secondly, the saturated vapor pressure of R134a is different from that of R12, and its compatibility with system seals varies. The nitrile rubber seals commonly used in R12 systems will swell and fail when in contact with R134a. Thus, the seals need to be replaced with those made of hydrogenated nitrile butadiene rubber (HNBR) or fluororubber. Meanwhile, aging pipelines and valves should be inspected and replaced to avoid refrigerant leakage caused by poor sealing. In addition, the heat transfer performance and flow characteristics of R134a are slightly different from those of R12. To ensure refrigeration efficiency, it is necessary to replace the system's drier filter with a type XH-7 or XH-9 molecular sieve drier filter suitable for R134a, to prevent ice blockage caused by moisture in the system. At the same time, the opening degree of the expansion valve or the size of the throttle orifice can be adjusted according to actual conditions to optimize refrigerant flow control. Finally, after completing component replacement and pipeline cleaning, the system should be evacuated to ensure no air or moisture remains inside. Then, charge the system with refrigerant suitable for R134a, strictly following the filling quantity specified in the equipment manual to avoid insufficient or excessive charging that would affect refrigeration efficiency.