Brussels, Belgium — March 6, 2009 — Excerpt from this R744.com article:
R744 versus R134a
The ASHRAE paper also mentions the hotly debated MAC issue where the currently used refrigerant R134a has a six times lower heat transfer capability than R744 at 14°C, the optimal temperature for transferring heat to R744. Thanks to its properties, the German Association of the Automotive Industry (VDA 2007) has confirmed that all mobile air conditioning (MAC) systems for cars will be fitted with R744 from 2011, when the European MAC Directive first deadline comes into force.

Use the link above for the entire article.