Airc Conditioning Kaput...Help Please

Any ideas?
Thanks
My air conditioner started acting up the other day. Sometimes cold air comes out, most of the time it just blows air. It looks like the compressor clutch is not engaging. I can set temp to coldest, and I don't think that the compressor is running. Engine does not change RPM when A/C is turned on and so on.
Any ideas?
Thanks


