Air conditioner is not functioning properly

I have a 2003 jaguar X series The air
conditioner is charged and not
leaking. When I turn the air conditioner
on in the car at idle it blows warm air
but going down the road when the
RPMs are up it blows cold air but not
real cold then when it drops down to
idle it’s blowing warm air out of my
vents what could be the problem with
that how can I repair it