The dishes on the top rack of our Frigidaire FDB2310LCC2 are not coming clean. I checked the position of the center wash arm and ran the dishwasher through a complete wash cycle. When it was done the arm had not moved. I did check the wash arm by putting a hose into the water supply and water flows through all of the ports on it, none of them are clogged. What can be causing this issue? Thanks, John