Model #MDB7600AWW, this tall tub dishwasher was not filling with water at the beginning of the cycle. The customer indicated the unit would make all the normal sounds, but it was obvious there was no water going to the unit. After verifying the usual water connections and valves, I got to work on the problem.
Most dishwashers will use an electric water valve which actuates to add water to the tub. These valves consists of a coil of wire that will act like an electromagnet when current flows through. The magnetic field produced will pull a metal core connected to the valve open allowing water to flow. When current stops flowing, the magnetic field will collapse and the water pressure from the line will close the valve.
The dishwasher control on this unit activates the water valve for a set period of time during each fill process. This is called a timed fill because the quantity of water that enters the tub is only determined by the length of time the valve is open. It is for this reason the dishwasher will still operate even with no water in the tub.
A quick way to diagnose this problem is to use a meter and do a voltage check across the valve terminals. Because this valve is an electrical load, if voltage is present but the valve isn't working, then the valve must be bad. If voltage isn't present, then the problem would lie somewhere else in the unit such as the control board. A resistance check can also be made between the valve terminals, and an open circuit there would also indicate a failed component.
On this unit, I had voltage to the valve, but no operation so I found the problem. Installed a new valve
assembly under this dishwasher (turned the water and power off first) then with everything back together started a test cycle. Water entered the tub as expected, and this customer was glad to be done washing dishes by hand.