From R-134a to HFO-1234yf, or is it R744?
Starting in model year 2013, car manufacturers are introducing in the air conditioner systems the new refrigerant HFO-1234yf (
HydroFluoroOlefins) (Photo 1).
This refrigerant will replace the existing R-134a in all vehicles no later than model year 2017. Since its GWP (Global Warming Potential) is far less harmful, it was deemed a good fit to replace the R-134a in use since the mid-nineties.
At this point, no conversion is possible from the retiring R-134a system to the newer HFO-1234yf because the pressure and filling connector are different. (Photo 2)
What then is going to change in repair shops?
Whenever one says new refrigerant, the echo says new equipment! Sorry, there is no way out. It was the same story when the R12 got sacked:
• Recovery, recycling and recharging equipment, in compliance with standard SAE J2843)
• Refrigerant analyzer and identifier, in compliance with standard SAE J2927
• Electronic Leak detector, in compliance with standard SAE J2913)
• New PAG (Poly Alkylene Glycol) oil
But let’s face it, it will take a few years before a customer drives up to your shop with a HFO-1234yf system requiring maintenance.
Although nothing is yet official – and nobody can provide an answer with certainty – some form of halocarbon certification will be mandatory to handle the new product. However, credible government sources (at least in Quebec) agree to say current certification will remain valid. On the other hand, more training and a new certification will be required in the United States.
At this point, Volkswagen and Mercedes-Benz have announced their dissent to the new refrigerant. They claim one main reason: the inflammability potential according to crash tests carried out with their own vehicles using the new refrigerant. This is why they have ordered Honeywell – who will also manufacture HFO-1234yf with DuPont – to develop an AC system based on CO2 (carbon dioxide, also called R744) before the 2017 deadline. It is a huge challenge, but they could reach their goal. And here is how:
In 2006, a few manufacturers created a functional CO2-based prototype AC system for motor vehicles (the food industry has used this system for ages). Used as an AC refrigerant, CO2 has an even better GWP than HFO-1234yf. Retiring R-134a shows a GWP of 1300 while CO2 is only 1 (HFO-1234yf has a GWP factor of 4). But, a small problem remains.
To operate properly, the prototype CO2 system was using an AC compressor with 2000 PSI minimum in the high pressure linkage and as high as 500 PSI in the lower pressure linkage. Just to get the system going, the engine required no less than 26 extra HP. At that time, it meant fuel consumption got a serious hike, using 15 L/100km instead of the usual seven. So, what was gained by not using the older R-134a was quickly lost in air pollution with excessive fuel spending.
So, why did Honeywell agree to commit some R & D to develop a CO2 system knowing very well that pressures had to remain so high? The possibility of using an electric compressor changed the game. If such a technology can be used in hybrid cars with an AC compressor operating on 500 volts AC, then maybe there is real potential for this system. This is the gamble Honeywell took and there are 3.5 years left before the deadline.
New heat exchanger
In newer vehicles working on R-134a, a heat exchanger was integrated to the AC system. Adding a thermal exchanger gives those systems much more efficiency.
There are many benefits when using this extra component:
• The AC compressor is not used as much, which trades off with a better fuel economy
• With this component, vehicles so equipped are much more efficient to eliminating warm air inside the cockpit.
• Compact component
• Low cost feature
• And finally, a plus for the manufacturer that has nothing to do with technicians or servicing: vehicles with a heat exchanger earn a 1,1 gram per mile credit towards the CAFE standards.
More precisely, how does the heat exchanger work:
Refrigerant exits the compressor in high pressure vapor mode to enter the condenser. (Photo 3) At this point, nothing is new. When transiting through the condenser, the refrigerant has changed to a liquid state under high pressure. Here, the high pressure linkage makes contact with the low pressure linkage returning to the compressor (see enlarged Picture A). High pressure hot refrigerant makes contact at this point with low pressure cold liquid and loses more heat in the process until it reaches evaporator (see enlarged Picture B). This additional heat loss will result in the evaporator with a larger capacity to pull out more heat from the cockpit.
Now, what about the pressures?
As a technician and shop owner, what kind of problem is expected in the future?
No need to read a crystal ball, but one can wonder what will happen to the heat exchanger when it reaches 200,000 km or seven years and thousands of cycles. With a high pressure liquid refrigerant flowing in the exchanger just millimeters of linkage away from a low pressure liquid zone, if there is a fracture inside the exchanger, then high pressure liquid refrigerant would be hard-pressed directly in the compressor.
The question is: can a compressor handle liquids? Out of the question. Should this happen, a complete destruction of the compressor is apprehended and no belt could resist an immediate blockage of the compressor. Let’s hope this never happens and engineers can prevent the havoc!
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