Refrigerators and air-conditioners are basically the same thing, a heat pump that transfers heat from one area to another. In the case of a vehicle air conditioning system, heat is transferred from the vehicle’s interior to the exterior.
There are two sides to the system, separated by the compressor and the expansion valve, one high-pressure and high-heat, the other low-pressure and low-heat. The system works because the refrigerant gas is compressed into a liquid on the high-side of the system, and then when it exits the expansion valve, heat vaporizes the liquid back into a gas.
Various substances can be used as a refrigerant, as long as they compress well into a liquid and vaporize in temperatures over about -20°F. Liquified petroleum gas [LPG], also known as propane, works really well as a refrigerant, but there’s a problem with flammability. Obviously, this is illegal, but is still practiced by unscrupulous people that haven’t a care for greenhouse gas emissions or passenger safety. In an accident, an illegally-filled air-conditioning system can explode.
The search was on for a refrigerant that wasn’t flammable, and eventually researchers came upon a new formulation called R-12. The only problem with R-12, though, is that it is a harmful greenhouse gas. Today, like LPG, R-12 is also illegal, and has been replaced by R-134a, another non-flammable refrigerant that isn’t as bad for the atmosphere. Still, R-134a is a fairly potent greenhouse gas, so a replacement is needed if we’re going to stave off emissions from this source.
Honeywell and Dupont’s new refrigerant, HFO-1234yf, is supposed to be better for the environment as well as be non-flammable, but some recent testing by BMW, Daimler, and Audi are having second thoughts in testing this new refrigerant in the automobile market. In fact, Daimler has already recalled some 1,300 Mercedes using HFO-1234yf after conducting crash tests. Crash test engineers found that the heat of the turbocharger was enough to spontaneously ignite the new refrigerant in the event of a frontal crash, the most likely to cause a rupture in the air-conditioning system.
The Society of Automotive Engineers [SAE] recently performed some of their own testing, and Honeywell fought back in a press release saying, “the refrigerant release testing completed by Daimler was unrealistic by creating the extremely idealized conditions for ignition while ignoring actual real world collision scenarios. These conditions include specific combinations of temperature, amount and distribution of refrigerant, along with velocity, turbulence, and atomization, which are highly improbable to simultaneously occur in real-world collisions.”
Honeywell doesn’t believe that HFO-1234yf is any more dangerous than other automobile fluids, citing the flammability and widespread use of automatic transmission fluid, engine oil, and of course, gasoline and diesel fuel. If this is the case, then we’ve nothing to worry about except reducing greenhouse gas emissions by 99.7% over R-134a. On the other hand, what if the perfect storm of circumstances occur and an HFO-1234yf air conditioning system explodes? Granted, this is a small chance, but are automakers willing to take the risk?