HIGH IDLE WHEN SWITCHING a/c/ ON

[greg geraci]

I'VE BEEN EXPERIENCING HIGH IDLE WHEN I TURN ON THE A/C COMPRESSOR. It used to idle at 900 rpm's in all conditions but lately it has risen to about 1200 and when I flip on the A/C compressor it jumps up to about 1800 and will not drop unless I turn off the A/C. And then it idles a little high around 1100. Is their any one that experienced this before or have a possible diagnosis.
thanks for your time,
Greg