Abstract A wearable cooling system was developed for use in elevated temperature environments by military, fire-fighting, chemical-response, and other hazardous duty personnel. The cooling system consists of an engine-driven R134a vapor compression system assembled in a backpack configuration, coupled with a cooling garment containing refrigerant lines. A 2.0 L fuel tank powers a small-scale engine that runs a compressor fabricated in house. The overall cooling system, including the wearable evaporator, had a mass of 5.31 kg and measured 0.318 × 0.273 × 0.152 m. Controlled environment tests determined system performance over a range of ambient temperatures (37.7–47.5 °C), evaporator refrigerant temperatures (22.2–26.1 °C), 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 calisthenics or moderate exercise, were demonstrated at an ambient temperature of 43.3 °C. The system consumed 1750 W at a fuel flow rate of 0.316 kg h −1 to provide a 178 W of cooling for 5.7 h.