Abstract: Air Cycle Machines (ACMs) are classified as high-speed turbomachines and nowadays, most of the Environmental Control Systems (ECS) on civil and military aircrafts are equipped with ACMs that use Gas Foil Bearings (GFBs). GFBs can be used in an environment different from air, like refrigerants in the ECS. Over the last 20 years, a significant number of studies have shown that GFBs represent the best options for a consequent range of applications. However, there are still problems when one tries to implement GFBs into new systems, particularly in refrigerant environment. Studies in this domain already exist but they are either experimental or analytical but without specific lubricant behavior analysis. Refrigerant-lubricated GFBs require a specific Thermo-Elasto-HydroDynamic (TEHD) theoretical and numerical model. In this paper, static and dynamic GFBs' behavior are investigated when operating in refrigerating gas. A TEHD approach is used in conjunction with gas constitutive equation to describe pressure, density, viscosity and temperature. It involves the use of a GRE (Generalized Reynolds Equation) for turbulent flow, a non-linear cubic EoS (Equation of State) for two-phase flow, a 3D turbulent thin-film energy equation, 3D thermal equations in solids and the foil distortion consideration. Journal bearings' global parameters are calculated for steady state and dynamic conditions.