Compressor only works sometimes

I have a 2000 Chevy blazer and just
recently the compressor stopped
blowing air but when I let it sit
overnight the air will work perfectly
fine I checked power going to the
compressor and there is power going
to it. I just have no clue as to why it
works sometimes and not others. I
plan on buying a new car soon but
lately this winter has been frigid,
hence why I don't want to bring it a
shop and be charged an arm and leg
for this. Any help is greatly
appreciated.