The development of a wearable cooling system for use in elevated-temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel is underway. Such a system is expected to reduce heat-related stresses, increasing productivity and allowable mission duration, to reduce fatigue, and to lead to a safer working environment. The cooling system consists of an engine-driven vapor-compression system assembled in a backpack configuration, to be coupled with a cooling garment containing refrigerant lines worn in close proximity to the skin. A 2.0 l fuel tank powers a small-scale engine that runs a compressor modified from the original air compression application to the refrigerant compression application here. A centrifugal clutch and reduction gear train system was designed and fabricated to couple the engine output to the refrigerant compressor and heat rejection fan. The system measured and weighed 4.46 kg. Testing was conducted in a controlled environment to determine performance over a wide range of expected ambient temperatures , evaporator refrigerant temperatures , and engine speeds (10,500–13,300 rpm). Heat removal rates of up to 300 W, which is the cooling rate for maintaining comfort at an activity level comparable to moderate exercise, were demonstrated at a nominal ambient temperature of . The system consumes fuel at an average rate of 0.316 kg/h to provide nominal cooling of 178 W for 5.7 h between refueling.