Аннотация:An upgraded version of the OGRAN - combined optical-acoustic gravitational wave detector- has been investigated in a long-term operation mode. This installation, located at theBaksan Neutrino Observatory (BNO) INR RAS, is designed to work under the program for detecting collapsing stars in parallel with the neutrino detector: - Baksan Underground Scintillation Telescope (BUST). Such joint search corresponds to the modern trend for a development of “multi-messenger astronomy”. In this work the effects of thermal relaxation OGRAN are experimentally investigated using passive and active thermal stabilization systems in the underground laboratory BNO PK-14.