The HFO-1234yf Cooperative Research Programs conducted in recent years at international laboratories investigated a range of issues including:
Safety and risk assessment
Air-conditioning system efficiency and performance
Material compatibility
Flammability
Toxicity
The extensive testing at third-party facilities did not identify significant risks for the use of HFO-1234yf in mobile air-conditioning systems.
Further information about HFOs is contained in
http://www.fluorocarbons.org/uploads/Modules/Library/15.03.2010_p.p.-hfos.pdf