Why does the car make a hissing sound when the air conditioner is turned on for a while?
3 Answers
The reason why the car makes a hissing sound when the air conditioner is turned on for a while is due to insufficient refrigerant. Here are some related introductions about air conditioner maintenance: 1. Choose the appropriate air conditioner temperature: When the temperature is set too low, it can affect health, so the air conditioner temperature adjustment must be appropriate. The most comfortable temperature for the human body is between 20°C and 25°C. Above 28°C, people will feel stuffy, and below 14°C, people will feel cold. Therefore, the air conditioner should control the temperature inside the car between 18°C and 25°C. Too low a temperature can easily make people sick. 2. Immediately activate the internal circulation when entering the car in summer: When you first enter the car, you should open the windows for ventilation and turn on the external circulation to expel the hot air. After the temperature inside the car drops, switch to internal circulation.
I recently encountered the hissing sound from the AC as well, like a gas leak from a valve. It's usually due to refrigerant leakage, possibly from a tiny gap in the AC system's connecting pipes or evaporator, causing the gas to escape with that sound. Causes include aging pipes, loose joints from vibration, or malfunctioning compressor valves. Last time I ignored it, the cooling effect worsened daily until only weak airflow remained. I recommend getting the refrigerant pressure checked at a repair shop to locate the leak and fix it promptly to avoid system failure. Avoid sudden braking or rough roads to prevent pipe damage from vibrations. Regularly replacing the AC filter can also stop minor issues from escalating.
As a driver who frequently takes long trips, I'm quite familiar with this type of sound. The deflation noise usually comes from the engine compartment at the front of the car, resembling the sudden release of pressure. This is often related to the operation of the air conditioning compressor: during normal startup, it may produce slight pneumatic sounds; but when abnormal, it could be refrigerant leaking from seals or valve plates, causing intermittent hissing. When I encountered this, I checked the pipeline surfaces for oil stains—a sign of refrigerant leakage—but the issue was hard to completely resolve. It's best to visit a professional shop early to test the system's sealing, otherwise, prolonged neglect may lead to AC failure, affecting driving comfort. This is more common during hot summer temperatures, and keeping the cabin ventilated can help alleviate the issue.
