The performance characteristics of a fast-axial-flow, rf-discharge-excited CO laser have been investigated in the operating temperature range of 240-290 K. The laser gas is cooled with a water cooler and/or with a commercial available refrigerator. Eight discharge tubes are optically connected in series, each of which is composed of a 19-mm inner-diameter quartz pipe and a pair of 300-mm-long outer metallic electrodes. They are geometrically optimized to obtain uniform excitation over the whole discharge volume. At room temperature, the influence of the operating gas conditions, the additives, and the impurities on the laser performance are examined. It is shown that the addition of Ar, instead of Xe. to the working mixtures (CO/N₂/He/O₂) drastically improves the laser performance. Finally, it is demonstrated that 40-50% higher outputs than that at room-temperature are obtained at temperature of 240 K, and the output reaches over 1 kW with the Xe-free, Ar-added mixture. The output spectrum and the beam characteristics are reported.