Prakash Thawani, Steve Sinadinos and John Zvonek DENSO International America Inc. Southfield, MI Abstract With the advent of EVs/HEVs and implementation of Idle-Stop-Start (ISS) technologies on internal combustion engine driven cars/trucks to improve fuel economy and reduce pollution, refrigerant sub-system (RSS) induced noise phenomena like, hissing, gurgling and tones become readily audible and can result in to Customer complaints and concerns. One of the key components that induces these noise phenomena is the Thermal Expansion Valve (TXV). The TXV throttles compressed refrigerant through the evaporator that results in air-conditioning (A/C) or thermal system comfort and defogging when needed. Under certain operating conditions, the flow of gas and/or liquid/gas refrigerant at high pressure and velocity excites audible acoustical and structural modes inherent in the tubing/evaporator/HVAC case. These modes may often get masked and sometimes enhanced by the engine harmonics and blower noise. Due to the seasonal demands on A/C compressor cycling ON/OFF, these noises since transient can be easily perceived in the vehicle interior. This paper presents a case study with a systematic approach to excite and quantify these noises induced by the Refrigerant Sub-System (RSS) at the bench-level in a laboratory environment with simulated vehicle operating conditions at a variety of thermal loads. This facilitates development of cost-effective counter-measures can be validated at the bench and implemented later at the vehicle level, if needed. Based on the sound quality analysis and listening studies of bench and vehicle level measurements, some sound quality metrics were investigated for their suitability as reliable objective targets that correlate well with subjective perceptions for the hiss and gurgle phenomena at an early stage of vehicle development.