I have a 2 year old Frigidaire dishwasher (model number FDB710LCB0). Before I start, I have cleaned all the filters and checked for obstructions. Now, the problem is this: During the Heavy and Normal wash cycles, the upper spout, which supplies water to the middle arm does not produce enough pressure to spin the middle arm. The lower arm has fantastic pressure. Only during the Light wash cycle does the upper spout really spray well, but only for about 30 seconds or so. Under the filter there is a small plastic ball which sits next to the impeller blade. The ball appears to perform the function of alternately plugging up either the upper spout path or the lower spout path, to allow each arm to operate one at a time (this model is supposed to have the two arms alternate spraying. I suppose the impeller is supposed to reverse direction (?) to cause the ball to travel back and forth on its ramp. I'm at a loss as to what is wrong. If I remove the ball, both arms work at the same time, but with reduced pressure on each arm reducing effectiveness. Any ideas?