Comfort parameters in the saloon of passenger train are an important criteria for the clients of passenger train operator – for the passenger. In some cases, this criteria can even be a reason to change transports means in favor or disfavor to railway in the winter time. It is an important goal to maintain stable and comfortable environment in the passenger saloon, irrespective of changes in train load percentage, ambient air temperature and operation mode, to attract as much as possible passengers to the railway transport. To solve this problem on the DR1AC series DMU trains modernised for the Latvian railways, an energy effective, combined air and electrical heating system is used, maintaining full compliance to requirements of passenger saloon environment, as laid out in standard EN 14750-1. Simultaneous regulation of temperature and microclimate in several passenger compartments with very narrow allowable parameter range is a complicated problem, thus an elastic and sophisticated regulation system was used, requiring initial set-up and testing. In this article particular notes of the initial setting and testing of heating and air-conditioning system of the DR1AC series DMU train are reviewed, carried out on the first modernized train in years 2015-2016, before transferring the train to certification tests.