The authors consider possibilities of the criterial approach to determining the current operating mode of a single-stage thermoelectric cooling unit (TCU), when used reliability failure rate as a basic parameter. The relations were obtained for determining the current operating mode of a TCU with a given geometry of the branches for different operating conditions, taking into account a variety of restrictive requirements. The paper presents a comparative analysis of current conditions close to the maximum energy efficiency and minimum modes failure rate, which allows choosing compromise options.