2004 BMW X5 compressor is not engaging

[aboaljood]

I have BMW X5 2004 4.4, the problem is when I start the car in the morning and the AC is on the compressor is not starting, then I have to push on the petrol until the RPM is up to5000 or more so it works.
and for the rest of the day every time I start the car I have to push petrol so the RPM is around 2000 so it works.
some mechanical told me it's the compressor but I couldn't believe that because when the compressor works, the air is freezing and it never stops until I switch the car off.
Has anybody experienced same problem or has an idea about this problem?