Here's a short and sweet case study for you. An Appliantologist was working on a GE washer with an inop drain pump, and so he ran some tests. We'll go through those tests, and as we do, the problem should jump out at you right away. 

First, here's the schematic of the drain pump:

Just a 120 VAC pump that gets Line and Neutral from the control board. Doesn't get simpler than that!

Here's the first test our tech did -- a voltage test with his multimeter from the Line to the Neutral pin on the board. Our tech did this and all his other voltage tests with the pump connected to the board and running in diagnostic mode.

His meter read 0 volts. Well, that immediately tells you that there's a problem with the power supply!

Next test:

This is showing a voltage test from the Line pin to chassis ground. Before we get to the results of this test, let me say that this is not how you should do this test. When doing AC voltage testing, you should never use ground as your reference. Ground is never an intended part of an AC circuit -- but Neutral is. So Neutral should always be your reference, and there's a conveniently accessible Neutral going to the inverter on this board: J506 pin 2.

Regardless, the result of this test was 120 volts. Well that's interesting -- so there is voltage standing on pin 2 of the drain pump connector.

If you're a sharp tech who's been around the block once or twice, you can already tell what the issue is. But our tech wanted to be thorough, so he carried on with some more testing.

Same test as before, but this time on pin 3 -- the Neutral pin. And he got the same result: 120 volts. 120 volts on Neutral? That's weird.

So, to recap: we have 0 volts from pin 2 to pin 3, but 120 volts from either pin to an external reference. Your spidey-senses should really be tingling now. But here are a couple more tests our tech did while you ponder:

A resistance test through the drain pump from the control read about 20 ohms -- in spec for this pump. According to ohms, at least, it's good.

But we know not to make diagnostic conclusions using ohms when we can avoid it, so for our final test...

...our tech hooked the pump up to a cheater cord directly connected to the wall outlet. And it ran just fine!

As I'm sure you saw, those last two tests were completely superfluous. The problem is obviously with the power supply to the pump, not with the pump itself.

So what is the problem? Well, if you haven't figured it out yet... it's an open Neutral.

How do we know? It's the only explanation for the readings we got. The reason our tech got 0 volts on his very first test from pin 2 to 3 is because he was reading from Line potential to Line potential. With an open Neutral, there's no current through the load, and therefore no voltage drop. That means you have your full supply voltage present from the Line pin, all the way through the pump, and up to the Neutral pin.

It would look like this:

Those voltage readings that our tech got were classic indicators of an open Neutral. Learn to recognize them, and you'll save yourself a bunch of time and headache with your troubleshooting!

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