In the event of chlorofluorocarbon (CFC) phase out, identifying a long term alternative to meet all our requirements in respect of system performance and service is an important area for research in the refrigeration and air conditioning (RAC) sector. Even though HFC134a and the HC blend (containing 55.2% HC600a and 44.8% HC290) have been reported to be substitutes for CFC12, they have their own drawbacks in energy efficiency, flammability and serviceability aspects of the system. HFC134a is not miscible with mineral oil, and hence, polyol ester oil is recommended, which is highly hygroscopic in nature. This hygroscopicity demands stringent service practices, which otherwise results in moisture entry into the system. On the other hand, the HC blend has flammability issues, and hence, the charge quantity in systems is limited by safety standards. This work focuses on experimentally studying the performance of an ozone friendly refrigerant mixture (containing HFC134a/HC600a/HC290) in a walk in cooler, operating with an open type compressor with mineral oil as lubricant. To have a realistic comparison of the new mixture performance, tests were conducted with the conventional refrigerant (CFC12) for the system behaviour, such as no load pull down time, motor power, energy consumption, ON and OFF cycle time, temperature distribution along the coil and COP. The performance of the system with the new mixture was studied and compared. The oil miscibility of the new mixture with mineral oil was also studied and found to be good. It is observed that the mixture has better performance, resulting in 28.6% less energy consumption than CFC12. The enhancement in COP was 6-10%. (C) 2003 Elsevier Ltd. All rights reserved.