A/C noises in engine bay - hissing after engine stop

[GriffX]

For the first time ever I refilled an A/C system myself, the temp coming from the vents was around 52F only so I used one of the refill bottles.
First pressure was around 20psi so right at the start of the green area of the gauge. I used a full bottle to get to 40 psi (according to the seller 45psi should be enough).
Today I noticed a hissing noise after I stopped the engine (A/C on) in the engine bay coming near by the firewall where the A/C lines goes through.
It is hissing for ~30 s after engine stop.

Is this normal?

Thanks!

 

[Juice]

Yes, normal.

 

[GriffX]

Yes, normal.

Thank you !