This paper reports the results from the development and performance testing of a cost effective, energy efficient, multi-type air conditioner that connected five indoor units (evaporators) to one outdoor unit (condenser) with a digital scroll compressor. Instead of using inverter technology, which has a potential risk of harmonic current emissions, this study used a digital scroll compressor, which provided the variable refrigerant volumes. The measured results for this innovative design showed: (1) The relationship between the degree of opening of the electronic expansion valves (s) and the compressor output ratio (%) could be represented by regression functions, which formed the basic parameters of the system control. (2) The developed system provided true zoning capability because it could run indoor units under part load conditions, therefore wasting little energy. The power consumption of the developed system was reduced from 100% to 25% when the full load was reduced to a partial load of 17%, saving more than 75% of the work required using a conventional un-loading method. (3) The developed system has a broader range of capacity output (from 17% to 100%) than that of an AC variable frequency control system (from 48% to 104%). The developed system cost 20% less than a comparable system with an AC inverter. (C) 2004 Elsevier Ltd. All rights reserved.