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Automotive refrigerant system induced noise and vibration transients usually accompany A/C compressor engagement/disengagement. These transients include audible/perceivable metallic impact/slip (clink, chirp, etc.), engagement thump, delayed accumulator thump, orifice tube/TXV induced hiss, and occasionally very loud slugging. In this paper, the inherent noise source mechanisms of these transients are described, and a set of psychoacoustics based objective metrics quantifying these transients in terms of loudness and sharpness is developed. Some of the recommended design-fixes and noise control approaches for the related transient noises are also discussed.

The refrigerant transition from HFC-134a to HFO-1234yf has proven to be more challenging on controlling refrigerant flow-induced noises generated from automotive air-conditioning (A/C) systems than originally anticipated. The objectives of this paper are to describe the noise issues with HFO-1234yf, understand the mechanisms and key factors affecting HFO-1234yf refrigerant flow-induced noise. Finally, the countermeasures and guidelines for attenuating and suppressing the noise are presented.

The automotive refrigerant systems can occasionally exhibit a transient hoot/whistle type noise under certain operating conditions. High pressure/velocity refrigerant flow through an evaporator core can readily excite the inherent acoustical and/or structural modes, resulting in audible transient tones. This condition if present can be experienced while driving away from a short stop and can last 2 to 10 seconds. The ambient conditions suitable for creating this noise are - moderate/high air-conditioning (A/C) load during days at 85-95° F temperatures with high humidity. Possible noise generating mechanisms have been discussed in earlier publications and our findings during this study indicate that they are excited by the high velocity superheated refrigerant vapor flow through the evaporator core plates. Examples of this transient noise and its spectral characteristics are presented to characterize this refrigerant system induced issue.