The COMmercial Experiment Transporter (COMET) is a satellite will launch aboard the Conestoga rocket. COMET provides the United States Commercial research and development community with a dependable and economical means to access space. The COMET program is defined and funded by the NASA Centers for the Commercial Development of Space (CCDS). The Center of Space Transportation and Applied Research (CSTAR) was given the authority to establish and implement the COMET program.The COMET Service Module is designed, integrated and tested by Defense Systems Incorporated for Westinghouse Commercial Space. The Capillary Pumped Loop (CPL) was integrated into the Service Module by OAO Corporation for Defense Systems Incorporated. The Service Module's primary function is to carry payloads to space, providing them with utilities such as a tightly controlled thermal environment, electrical power, attitude control, data management, and communications while in orbit.The thermal control requirements for COMET provide special and unique challenges for the thermal system test. The Service Module is required to maintain the experiment payload environment at 22.2°C ± 2.8°C on the launch pad, during launch, and for two years after orbit insertion. The thermal control system is required to operate in 1-g, in the earth and sun satellite 0-g orientation, on the launch pad. Subsystem testing also included defining reliable restart scenarios. This paper presents the results of functional and performance testings of the CPL Thermal Control System (TCS) for the COMET Service Module.