CO2 has much higher operating pressures and temperatures than medium pressure halogen refrigeration fluids, thus involves extreme mechanical constraints on moving components and bearings.

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Consequently, in tcase an unsuitable oil is used, the result of insufficient lubrication can be a premature wear of the system and a leak with a consequent loss of compression.

Basic addittivated POE molecules or PAG molecules will be more suitable for R-744 and may be suitable in subcritical and transcritical applications.