ac compressor not turning

I ahve a 93 astro van. last year the a/c worked no problem. I went to chcarge the system and the compressor is not locking. I know there is a plug to the compressor and i checked for power and there is no power there as i have the ac on max as i tried to charge the system. Now i know there is a a/c relay and fuse where would that might be so i can check it cause under the dash all i see is a a/c-heat circuit breaker.