electrical problem AC?

I have a steady drain of 12v on my car(1994 aspire). There is a clicking sound coming from the ac compressor when I hook up the battery. It goes away if i unplug the compressor, but there is still a drain on the battery. Is there some sort of relay somewhere that I just can't find, Does anyone have any ideas,
It will drain a fully charged battery overnight.
any help would be appreciated. John