A thermal control unit for controlling a patient's temperature includes a fluid outlet for delivering temperature-controlled fluid to a patient, a pump, first and second cooling units, and a controller that selectively enables and disables at least one of the cooling units based on one more factors, such as the temperature of the fluid. Alternatively or additionally, a variable speed fan is included in one or both of the cooling units that blows air over the condenser and the controller selectively controls the fan speed based on factors such as the temperature of the circulating fluid. The thermal control unit may be modified to accept a cartridge having its own cooling unit. When so modified, the controller communicates with a controller inside of the cartridge and coordinates control of the cartridge cooling unit and the cooling unit inside the thermal control unit that is external to the cartridge.