AC Compressor - small leaking sound

[geoff.doctor]

Just picked up a 1990 legacy wagon. When I bought the vehicle I noticed there was no belt on the compressor, and no charge in the system and it was pretty difficult to turn the clutch. Went to the junkyard and bought a used compressor for $20. This car was only $400, so I didn't want to spend a ton. I disconnected the old compressor, replaced the o-rings going into it, drained the oil out of the junkyard one, installed it, added some PAG oil and charged it up to the right level. It seems to be working fine, but when I shut off the car I can hear a VERY SLIGHT hiss coming from around the compressor. It makes this noise for about 30 seconds, then I can no longer hear it. Is this normal behavior for a compressor, or do I have a small leak? I cannot see, or feel the AC come out, and the pressure does not seem to decrease.

Any advice is appreciated.

[vrg3]

This is common. The high side and low side pressures are slowly equalizing. No problem.

[Legacy777]

You say you charged it up......I'm assuming you pulled a vacuum on the system before you charged it up right?