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What Causes the Hissing Sound When the Car Air Conditioner is Turned On?

2 Answers

VonRachel

07/30/25 1:55am

Car air conditioner abnormal noises are generally caused by internal or external issues within the air conditioning system. Internal noises typically occur when there is air or moisture in the refrigerant, leading to abnormal sounds during refrigerant evaporation and expansion, which users perceive as coming from inside the dashboard. External noises are usually due to issues with the air conditioner compressor, where the sound can be heard near the compressor. Below are other possible causes of abnormal noises in car air conditioners: 1. Contaminants in the refrigerant: The noise is often caused by air or moisture mixed into the refrigerant. 2. Damaged internal structure of the compressor: If the noise persists after refrigerant recharge and is located near the compressor, there is a high probability of internal mechanical damage to the compressor. If the noise recurs after some time and originates from inside the dashboard, it is likely due to reduced efficiency of the dryer. The noise heard after starting the air conditioner is primarily the operational noise of the compressor and does not indicate a fault.

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JayceLee

08/15/25 7:49am

One of the fairly common reasons for a hissing sound when the car's air conditioning is on could be refrigerant leakage, as the refrigerant makes a hissing noise when flowing through the system, similar to air leaking from a small hole. I once encountered a similar situation while driving, and it was a bit annoying because it reduced the cooling efficiency of the AC. Additionally, if the compressor is worn out or malfunctioning, it may produce similar noises during startup or operation. Blockages in the evaporator or condenser pipes or damaged valves can also cause airflow disruptions, leading to such sounds. I suggest first checking the refrigerant pressure to see if there’s a leak. If the noise appears suddenly, it’s best to take the car to a professional repair shop as soon as possible to avoid minor issues turning into major faults. Regular maintenance of the AC system, including cleaning the pipes and checking seals, can help prevent such problems. Overall, this isn’t just a noise issue—it affects safety and comfort, so don’t ignore it.

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