Sound of a Car Evaporator

‌1. Preparation for Detection Environment‌ Park the vehicle in a quiet environment, close windows, and turn off audio systems. Start the engine and activate the air conditioning in cooling mode A/C on.Adjust the airflow to medium to ensure the evaporator operates under normal working conditions‌.   ‌2. Sound Identification Methods‌ ‌‌Initial in-cabin auditory inspection‌‌ Listen carefully near the air vents inside the cabin for the following sounds:Friction/vibration noises‌: Metallic clanking or grinding sounds may indicate mechanical damage or loose components in the evaporator‌. ‌High-pitched "squeaking"‌: Persistent sharp noises may signal abnormal refrigerant flow through the expansion valve (distinct from normal expansion noises)‌.     Auxiliary external inspection‌‌ Open the engine hood and locate the evaporator (typically near the firewall under the dashboard,such as the evaporator for Honda Fit 2008 as below). Use a stethoscope or hollow tube pressed against the evaporator housing to isolate abnormal sounds‌.Intermittent "gurgling" or "bubbling" noises may suggest refrigerant circulation issues, blockages, or icing inside the evaporator‌.   ‌ 3. Normal vs. Abnormal Sound Comparison ‌Sound Type ‌Characteristics ‌Normal expansion valve  Soft, rhythmic "hissing" that varies with compressor cycling; non-irritating. ‌Abnormal friction/vibration  Persistent metallic scraping/clanging, often accompanied by steering wheel/dashboard resonance‌. ‌Refrigerant circulation issues  Flowing water-like sounds, intermittent buzzing, or bubbling due to low refrigerant, ice buildup, or blockages‌.   4. Professional Diagnosis Recommendations‌ Differentiating Interference Factors: The "whooshing" sound of the air conditioning blower and the low hum of the compressor operating normally are both typical. Abnormal Handling: If unusual noises are detected, it is recommended to first check the refrigerant pressure, the surface of the evaporator for ice formation, or use fluorescent dye to detect leaks. If unable to determine the issue independently, professional equipment (such as an electronic stethoscope) should be used to locate the fault point.