PRECAUTION PRECAUTIONS FOR REFRIGERANT HFO-1234yf (R1234yf) (a) Compatibility (1) The parts used in the refrigerant cycle, etc. of the HFO-1234yf (R1234yf) system are not compatible with the conventional HFC-134a (R134a) system. (b) HFO-1234yf (R1234yf) Refrigerant (1) Always use HFO-1234yf (R1234yf