Hissing aircon

[golfvr6]

This is not on a mk4 golf, but on a new passat so here goes...
After driving the car for a while with the aircon on, when i stop and turn the engine off, there is a hissing noise coming from the bulkhead. It doesn't do it unless the aircon has been on.
I was just wondering if this is normal, vw say it is, but i'm not sure.
Cheers guys  

[topher]

is it aircon or climate ? my climate hisses but it stops when i turn the engine off..

[golfvr6]

Its got climate control.
It hisses for about 20 seconds after i turn the engine off.

[topher]

i'll check tomorrow then, i havent paid attention before to be honest, i'll let you know.

[golfvr6]

Ok thanks.
At first i thought it was the coolant expansion cap letting off steam, as thats what it sounded like, thats bad as it could mean a blown head gasket (what happened to the 6).
But it is deffo coming from the bulkhead.

[shagmeister]

Hi! A gentle hissing from the aircon noise after you shut the ignition off  is normal, the aircon uses a compressor to push the refridgerant against a restriction, the expansion of the refridgerant after this giving the cooling effect.  So it is normal for the aircon to "gently" hiss, it is the pressure between the compressor and restriction equalising throughout the system, however i have a noise from my aircon which isnt normal, it sounds like a fan rubbin when u shut the aircon off, its going into the main stealers next week for diagnosis, bloke said he thinks its a common fault and under warranty, although he wouldnt be drawn on what this common fault is, when i find out will let you all know cheers shagmeister