R744 is the refrigerant name for carbon dioxide, which first appeared in high-end cars from German brands including Mercedes-Benz and Volkswagen Group on the European market.

CO2 requires operating pressures up to ten times higher than R134a. Although it has been used for some time in stationary equipment, getting R744 systems to work for automotive applications has been a significant engineering challenge, with unique components and system layouts required for this refrigerant.

The high pressures involved bring their own safety considerations when working on R744 systems.

As a result, working with R744 will require new service equipment meeting the relevant SAE standards, as well as technical training about the major differences.

The decision by some automotive manufacturers to adopt R744 came from flammability concerns about R1234yf, particularly Mercedes-Benz parent company Daimler. Mercedes-Benz was first to market with R744 systems in the S-Class but has since dropped it from internal combustion vehicles.

Volkswagen Group’s Audi A8 and electric vehicles based on the MEB platform also use R744 on certain variants sold on the European market.

However, the performance characteristics of R744 are not suited to hot climates and while some grey import cars with this refrigerant have made their way to New Zealand and required expensive, complex repair and recommissioning work, official imports of cars with R744 systems to Australia is unlikely.