Why do I not get water to the top shelf and how do I fix it

Most dishwashers either shoot water to the top shelf through a center tube, or they pump water to the top shelf through a tube at the back of the dishwasher. If your dishwasher has a large hole on the top of the lower wash arm, then it probably shoots water up through an expanding plastic tube to the upper shelf. That hole can get clogged, the expandable plastic tube can get stuck, or dishes can block the expansion of the tube. Any of these problems prohibit the water from getting to the top shelf properly. Check to make sure the expanding tube is free and clear, and that there’s nothing blocking any of the openings in the wash arm. If your dishwasher has a tube towards the back that carries water up to the upper rack, then you’ll need to check for any blockage in those tubes. That’s probably best left to a professional since you have to dissemble the tubes to check them.