Upper rack not cleaning, spray bar not spinning. I have left white vinegar in machine overnight and refilled with white vinegar solution and ran m/c on a hot cycle in the morning. Upper spray arm remains stationary. Water is flowing from the spray arm but at no great pressure. All filters are clean. There is no deberary in the spray arm. I suspect that not enough water is being 'switched' to the upper basket. Is this the component responsible for switching water flow to the upper basket/spray arm?