Abstract: An improved system for and method of precisely controlling the temperature at a predetermined location at a preselected temperature selected from a range of temperatures is described. The preferred system for carrying out the preferred method includes a mixing valve for separating a fluid stream into first and second component streams and adjustable in response to a first contol signal so as to control the amount of separation of first and second component streams. The preferred system also includes a heater for heating the first compponent stream in response to a second control signal, a first evaporator for cooling the second component stream and a conduit for combining the heated and cooled component streams so as to provide a mixed stream to the predetermined location. The first and second control signals are provided as a function of the preselected temperature, the temperature of the heated first component stream, the temperature of the mixed stream and the temperature at said predetermined location.