BACKGROUND: Designing a combine harvester cabin climate system is a complex and multi-stage process that includes solving a set of tasks. To solve the tasks set, a design engineer must have knowledge and skills in various fields, starting with thermal engineering calculations and ending with experimental research methods and computer modeling, which requires a large amount of intellectual and time resources. Therefore, the task of creating a unified combine harvester cabin climate system design methodology is very relevant. AIMS: The purpose of this work is the calculation and design of a climate system for a unified cabin of a grain harvester and a forage harvester. The designed climate system is designed to create a comfortable microclimate in the cabin of the combine for 2 people in summer and winter operating conditions. METHODS: The methodology of development of combine harvester cabin climate system is considered, which includes the development of engineering calculation methods and mathematical modeling of thermodynamic and ventilation processes in the cabin. RESULTS: The main parameters were determined: heat intakes and heat losses for the grain harvester and forage harvester cabins, which amounted to 2.8 and 2.2 kW for the grain harvester; 2.9 and 2.35 kW for the forage harvester; the required air flow rate supplied to the cabin to ensure a comfortable temperature – 740 m3/h; the percentage of air recirculation from the conditions of absence of fogging and creation of overpressure in the cabin – 75 %; the cooling and heating capacity of the climate system, taking into account the operating conditions of the combine, is 7.8 and 6.3 kW, respectively. The selection of the main equipment of the climate system for a unified cabin for a new family of unified cabins of combines – evaporator-heater BUHLER 1000 MFWD; compressor Valeo TM16. CONCLUSIONS: Designed in accordance with the presented climate system methodology, it will ensure a comfortable cabin air temperature in the range of 22-24 °C under various operating modes of the combine in different regions. In addition, the climate system parameters will eliminate fogging of the cabin windows and, due to the created overpressure, the penetration of dusty air inside.