What R-134a is and where it is used
R-134a (HFC-134a, 1,1,1,2-tetrafluoroethane) is a single-component HFC with properties very similar to R-12, which it replaced. EPA says automakers began moving from R-12 to R-134a with 1992 model year vehicles, and by the 1995 model year all new US vehicles with air conditioning used it. Arkema lists automotive air conditioning, chillers, medium-temperature commercial refrigeration, refrigeration appliances and transport refrigeration as its uses, and notes it is also a component in blends that replace R-502 and R-22.
It is ASHRAE safety group A1 with zero ozone depletion potential. Its 100-year GWP is 1430 (AR4) or 1300 (AR5), and EPA now restricts it in new cars, household refrigerators and several other kinds of new equipment.
How to read the R-134a chart
As a single compound, R-134a has one pressure per temperature, and the same column serves superheat and subcooling. It boils at -14.9°F at atmospheric pressure, so low-temperature rows read in inches of mercury vacuum: at -20°F the chart shows 3.7 in Hg vacuum.
- Superheat: a suction reading of 30 psig converts to 34.6°F. Subtract that from the suction line temperature.
- Subcooling: a liquid line reading of 150 psig converts to 111.5°F. Subtract the liquid line temperature from it.
The superheat calculator and subcooling calculator do the conversion. How to read a PT chart explains the method.
Example R-134a pressures
Pressures follow the saturation temperatures in the coils. The figures below are worked examples at assumed coil temperatures, not specifications for any vehicle or unit:
- Low side: an evaporator at 35°F reads about 30.4 psig. A refrigeration coil at 20°F reads about 18.4 psig.
- High side: at 110°F and 120°F condensing temperatures, R-134a reads 146.4 psig and 171.2 psig.
For a vehicle, the manufacturer's service information governs. For stationary equipment, follow the installation manual.
Service notes
- Oil: Arkema says R-134a needs POE, or PAG in automotive A/C only, because it does not mix with mineral oil or alkylbenzene. Both oils absorb moisture when left open to air. Arkema adds that in automotive systems POE and PAG are not interchangeable and should not be mixed.
- Charging: R-134a is a single compound, and Arkema says it can be charged as vapor or liquid. Follow the equipment or vehicle maker's procedure.
- R-12 retrofits: Arkema says to replace the old oil with POE, except in some automotive retrofits that require PAG, and in most cases to reduce mineral oil or alkylbenzene below 5% of the new POE charge. EPA says R-134a is the primary refrigerant used to retrofit R-12 vehicle systems.
- No mixing with R-1234yf: Chemours states that Opteon YF (R-1234yf) cannot be used for retrofit applications, so it does not go into an R-134a system.
Regulations and replacements
Under EPA's Technology Transitions rule, new light-duty vehicles from model year 2025 cannot use an HFC with a GWP of 150 or more in their A/C, and the same limit reaches medium-duty passenger vehicles, heavy-duty pickups and complete heavy-duty vans in model year 2028. EPA says R-1234yf is now used in the majority of light-duty vehicles. The rule also restricts R-134a in new household refrigerators, vending machines and stand-alone retail food units from 2025, and in new comfort-cooling chillers from 2025. Existing cars and equipment can still be serviced with R-134a.
For stationary retrofits, Chemours offers R-513A as its lowest-GWP retrofit refrigerant for R-134a systems, with no change of oil or seals; minor TXV adjustment may be needed. For cars, see R-134a vs R-1234yf: the two run close at 40°F (35.0 psig and 38.4 psig).