how do you replace a low side pressure switch for the ac on 2003 Chevrolet Silverado 3500

would like a diagram of what it looks like

First tell us why you think it needs to be replaced, since you don't know what it looks like. This is a pretty reliable part. Wire connections is most of the problems i see. Might help more if you tell us a bit more! Just tring to help you FIX the problem.