R-404A, which had long been used as the refrigerant of a unitary ice maker, has to be replaced due to global warming. In the present study, drop-in tests were conducted for long-term alternative refrigerants R-455A and R-454C on the ice maker of 100 kg/day capacity. Five samples were made having different combinations of refrigerant, condenser and compressor. Tests were conducted changing the outdoor and the supply water temperature. At the standard outdoor condition (21∘C, 65 RH and 10∘C water temperature), change of refrigerant from R-404A to R-455A for the same ice maker extended the ice ball formation time by 13% and reduced the amount of ice production per day by 6%. Larger vapor density and smaller temperature glide of R-404A may have resulted in a better performance. Furthermore, adoption of a larger (from 1/3 HP to 3/8 HP) compressor reduced the ice ball formation time by 12% and increased the amount of ice production per day by 8%. In addition, change of the fin-tube condenser to the microchannel condenser reduced the ice ball formation time by 9% and increased the amount of ice production per day by 4%. The refrigerant charge was also significantly reduced from 440 g to 316 g. Thermal performance of R-454C was poorer than that of R-455A. Replacement to R-454C increased the ice ball formation time by 14% and decreased the amount of ice production per day by 8%. The reason may be attributed to a larger pressure lift, which leads to smaller refrigerant mass flow rate. Ice production was possible even at the harsh environment (35∘C, 65 RH and 21∘C water temperature), although the production amount decreased.