Dishwashers aren’t that complex, no really!

Greetings Blogosphere,

Hello fellow DIY’ers.  You’ll find that as this blog evolves, I’m going to get into a lot of talk about home and auto repair.  You know, I can’t understand why we in this country have lost the will to repair things instead of getting new ones.  I think part of it is that manufacturers just push the marketing that you need the new latest greatest, but part of it is just our own laziness.  The average American is up to their eyeballs in debt these days, but their only response to a crisis like “my dishwasher broke” is to just whip out the plastic and forget about it until the next statement comes.  Well, I’m fed up with that answer.  So even if I have to go appliance by appliance, I’m going to help the average Joe understand just how not complicated these things are and prove that you can indeed fix it yourself if you try.

Today’s Lesson – My Dishwasher broke and tripped the breaker

I was on a business trip recently and got a call from my lovely wife that the dishwasher tripped the breaker that it’s plugged into at the main electrical panel.  The first thing I said was “why do the things always decided to wait until I’m gone to break!!”  After that I set out to working trying to help her with some troubleshooting.  Since our dishwasher is connected to a GFCI, I had her check to make sure the GFCI wasn’t tripped, which it was, and go out back to check the panel for a tripped breaker.  It was indeed tripped.  After resetting the breaker, I had her to try to start the dishwasher again.  Unfortunately for her, it tripped again immediately after pressing the start button.  She relented to having to hand wash dishes until I got back, and upon my return I embarked on a repair journey that was surprisingly shorter than I would have imagined.

Day 1 – The technical gathering and troubleshooting

Once I returned from my trip I immediately set to work on the dishwasher.  One of the most important things to do first when working on a machine is to learn what you can about it.  That means first of all reading the manufacturing label in order to obtain the model number of the unit.  In my case I was working on a GE dishwasher model PDW7880G00SS.  You can usually find this information on major appliances by peeking inside the door of the appliance.  This works for things like microwaves, ovens, fridges, etc.  Having this model number is important in the case where you have to buy parts from an online store.  Many parts retailers such as coast appliance parts allow you to enter the model of your dishwasher and obtain lots of cool things like blown up diagrams with part number and sometimes even schematics.  To start troubleshooting an appliance you have to start thinking like one.  By that I mean you have to think about what happens when you turn on the machine.  What order are the things that happen electronically.  A dishwasher is nothing more than a state machine, in that it has defined states based on inputs from the user and sensors.  It simply moves from state to state until the cycle is complete and waits for you to start the process again.  With that in mind, I took a careful listen to what happens when I start a cycle.  Here’s what I noticed:

  • Usually, when I start a cycle, the first thing that kicks on is the water inlet valve that lets hot water into the wash chamber.  This happens a number of seconds before the motor starts running.  It’s a definite “CLICK” once you start the cycle, and you can hear water flowing through the valve.
  • Today when I pressed “start” button on the washer, there was no “CLICK” and the breaker immediately tripped.  Since the first thing that happens in the cycle is the water fill, I figure I may be on to something here

Finding the water inlet valve

I plugged my model number into the old Googles, and found some really useful diagrams that physically represent my dishwasher.  Here’s the diagram I found, and it shows exactly where the inlet valve is.

Once that was done, I was able to get to that little beast without even removing the unit from the counter. I just pulled the kick plate out of the front of the unit, and got a clear view of the valve and wiring attached. This type of valve is known as a solenoid valve. That’s fancy engineer speak for the fact that the valve is actuated electronically via 120V power. The 120V signal turns on a coil which pulls the valve stem open and allows water to flow.

Here is the water inlet valve in blue, but this is controlled by a solenoid.

Testing for Failure

As luck (or good design choices) would have it, my valve’s solenoid had a connector. The simple way to narrow this device down as the culprit is to simply unplug it and see if the breaker stays on. After trying this, the breaker did indeed remain on while the dishwasher continued to run it’s cycle (without water running in). Now that we know this is the culprit, we know what to replace. Or do we?

You can see the red connector for the solenoid and the diode in black heatshrink.

See, here’s the thing. Most appliance repair people would just pull the valve module and replace it. this is fine, but that part costs $100 and takes a week to get it. I noticed that this valve has a flyback diode on it. After some close inspection, I could see that there was a physical hole in the diode noting that it had failed. Usually these types of diodes fail as a closed circuit which is the sort of thing that would cause a breaker to trip. I was highly suspect that this diode was what was causing all the problems. For more information about flyback diodes check this page out:

This diode is a real jerk. After peeling back the heatshrink it was a breeze to find that part on Digikey!

Simply using a multimeter can tell you the state of this device, and clearly it was stone dead. There was no voltage drop in the diode test, and the circuit read a dead short. Now that I knew what the problem was, all that was left to do was get the part. This was less than $2 and can be had on any major parts website. My choices:

After splicing that diode back in with some butt splices, and using some water-proof heat shrink to cover it all up, the repair was complete. Press the start button, and huzzah! No more tripped breaker. It’s amazing what $2 and a little patience can do.

The finished product, complete with non-tripping breaker
The finished product, complete with non-tripping breaker

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