Volvo s40 1.6 2001

I have a very difficult problem and to be honest it’s the first time seeing something like that.
The rpm in idling are fine in all conditions cold, warm, ps operation the problem is only with ac on.
The engine is running about 800rpm with ac off. After I switch on the ac the rpm increases to 950-1000 rpm and that’s very normal.
When I pressed the pedal to accelerate the idle valve keep up the rpm near to 2000 rpm and this is continued all the time that the compressor clutch is lock after that every time the ac compressor lock then rpm are increases near to 2000 rpm.

No trouble code stored.
The Idle valve is fine.
A/C pressure sensor is new.
Service air condition is done.

Any ideas Guys?

Idle reving up and sticking plus bad fuel consumption can be caused by crankshaft speed sensor. My dads car was also a 2001 1.6 what it happened to. Eventually if it is that it will throw a light. Might be worth just changing it as its only £30 and very easy to do.