Model # MDB7600AWW
, this tall tub dishwasher was making all the normal sounds during operation, but the customer said the dishes were not getting cleaned at all. It didn't seem to matter which cycle was run or where the dishes were located within the tub, it all came out looking like it did when it went in. But the information that gave me the lead on the failure, was the soap remaining in the dispenser when the load was complete.
Dishwashers are pretty basic in their operation. They fill with water, spray that water around, then drain the dirty water. Ideally while all that is taking place, the dishes will get rinsed off, and soap will get added at the appropriate time to help wash those dishes clean. Most dishwashers go through a preset series of cycles and follow a specified process to fill the tub, recirculate the water, heat the water, open the dispenser, and drain the water all without actually verifying anything is going on. Because of this, it is common to find a dishwasher that runs through a complete cycle without even adding water, or turning on the wash pump. The controls are simply following a preset series of steps until it gets to the end.
The customer of this unit said everything sounded normal during the cycle, but the dirty dishes are an indication something is amiss. I started a wash cycle and verified water was entering the tub, then listened to the wash pump as it kicked into action. One of the things I will do on any dishwasher is to align all the wash arms prior to starting a cycle. This way, I can tell if water is getting to them, or maybe getting blocked along the way. The results of this initial test was all three wash arms were still in the same place I left them when it started telling me there was no water getting pumped. The soap remaining in the dispenser is another good indication of no water from the spray arms.
Water is pumped by the wash motor via an impeller that is mounted below the lower wash arm. This can be easily accessed by removing what seems like way to many screws holding the various filter rings to the base of the tub. Once down to the impeller, it is difficult to tell if it works or not, but if you remove the mounting screw and look at the shaft, you can probably tell rather quickly. The original shafts were made of nylon and held the chopper blade in place while spinning the impeller. The usual scenario was something hard that shouldn't have been in the dishwasher in the first place finds it's way to the chopper and locks up the blade. This results in the blade and impeller stopping, but the fast rotation of the motor shaft breaks the nylon shaft and then just keeps spinning. Leaving us with a working motor, but a shaft with not enough bite on the motor shaft to pump much water. Without water pumping, the wash arms will never move and the dishes simply get a sauna.
Fortunately, there is a kit for these models that includes a new shaft and seal, and this time the shaft is metal and less likely to fail. I installed the seal kit into this dishwasher, and with everything put back together, it is now washing dishes better than ever.
Dishwasher Motor Seal Kit Part # 6-919539