L322 Air con compressor replacement

hi all
My air con compressor clutch had fallen off due to the bolt coming out (I think, bolt wasn't in it)
Replaced compressor today with a guaranteed used one.
My question is this, when I press the aircon button should the revs alter?
They don't, in fact nothing seems to change at all.
I haven't had it regassed yet as I want to know it's working as it should before I do that.
I had the gas removed prior to removing the old compressor
Thanks in advance

If there's no gas in it, the revs won't change as it won't even try to pull the clutch in.
With gas in, you might detect a slight change in engine note but the revs should stay more or less the same.

Ah ok thanks. I'll get it in on Saturday for the re-gas

On a big bored BMW V8, the revs will drop a tiny fraction....not a lot, but almost imperceptible