noises to hear
AC expansion valve

The hissing sound is caused by equalizing pressure. All cars even same models sound different


When the car AC system is running there is a high pressure side and a low pressure side that is divided by either an expansion valve or an orifice tube. This is noise is coming from the ( make that the passengers side ) floor well under the glove box.

When the vehicle is turned off or the air-conditioning compressor clutch is disengaged the system will equalize the pressure. The hissing sound is the ac gas from the high pressure side slowly feeding into the low pressure side and this is a normal condition.

Another air-conditioning noise would be the sound of the condenser fan. When the air-conditioning is running the condenser fan will pull additional air through the radiator and the condenser. This can cause additional noise that is not present when the air-conditioning is turned off. Often this additional noise is sensed as a problem by the driver.

Neil MMS