After running my AC while driving, then shutting off the car, the AC makes a lot of noise (hissing sound for quite awhile). It sounds like the compressor is de-pressurizing (not sure if word, lol).

I've never had this loud of noise on any of my other cars (some, but not this loud). Not sure if this is abnormal, or everyone experiences the same?

 

When system is running, the high side pressure is over 200 psi and low side is <30 psi. Pressure drop occurs across expansion valve (small variable opening refrigerant metering/cooling valve). When you shut down, pressure equalizes through the expansion valve opening. Because there is no other noise, you can hear the refrigerant flowing through the valve. Most ac systems do this to some extent.

good luck

 

Thanks Texas. Maybe the noise is greater than I am used to hearing since the TSX may have a greater pressure drop than other AC systems (or the expansion valve is just a different design).