Do you know what parallel circuits are and how they work? How about diodes? Here’s a snippet from an actual schematic for a Frigidaire wall oven, exactly the kind of circuits you would encounter on a service call. Let’s see whatcha got!

If you don’t get it, don’t feel bad– sadly, most of your fellow appliance techs, even guys with 20 years of experience, don’t understand this stuff, either. We can help you master basic electricity, series and parallel circuits, reading schematics, electric motors and more in our comprehensive, self-paced, online Fundamentals of Appliance Repair Training course.

We’ll take you way beyond the simple stuff, like the circuit above, in our Advanced Schematic Analysis and Troubleshooting (ASAT) training course. You can optionally bundle the Basic Electricity Boot Camp with the ASAT course for a top-notch electrical education specifically tailored for appliance techs using real-world examples from modern appliances.

Now for the answers to the quiz…

I’ve heard all kinds of crazy theories from techs about what happens when the diode opens. I’ve had guys tell me, “If the diode opens, it causes extra current to flow through the convection motor because current takes the path of least resistance and so it’ll burn out the convection motor.”

That is one of the more absurd examples of what I call “appliance tech mythology.”

You have to start with the understanding that electric current is nothing more than dumb electrons moving in a directed flow. Why do I say electrons are dumb? Because some techs seem to think they have a mind of their own and move in strange and mysterious ways.

The reality is that electrons move when, and ONLY when, there is a voltage difference between two points and they have a complete circuit. Electrons, being negatively charged, will be pushed away by negative voltage and “sucked in” by positive voltage. Provided there’s a complete circuit (no breaks or opens), the electrons will move in response to that voltage difference as surely as water flows downhill. It’s really that simple. Keep this in mind when we look at parallel circuits…

In parallel circuits, the voltage in each branch is the same. That’s just the way parallel circuits work. It is the voltage in each branch that drives the current– those electrons– through that branch… IF there’s a complete circuit for the electrons to flow.

So in the circuits above, if the diode failed open, the electrons can’t flow through that branch anymore because there’s no longer a complete circuit.

What happens to the voltage in that branch with the open diode?

Nothing, it stays the same.

What happens to the current in the branch circuit with the open diode?

It goes to zero because the electrons can’t flow anymore.

So what happens to the convection element?

It stays cold.

Alright, now what happens to the voltage in the other branch with the convection motor?

Nothing. Why should it change? It is the source voltage, 120 vac, and it stays the same as long as the power stays on.

Well, if the voltage in that branch stays the same, what happens to the current in that branch? You got it: it stays the same. See, you catch on fast! Ah, my fine young apprentice, you would make a star student in the Samurai Tech Academy. I could teach you all my tricks and you would become a certified Master Samurai Tech!

Okay, now the bonus question: What’s the function of the diode in the convection element circuit?

Well, to answer that, you first have to know what diodes do. They can actually do lots of different things but this particular one is a rectifying diode. How do I know that (we’ll get to what that means in a minute)? Because the schematic calls out the diode type: MR754. Google it.

What does a rectifying diode do? This:

The AC power comes in as a full sine wave but gets half its cycle chopped off by the diode. That’s because the diode is forward biased during half the AC cycle, keeping the circuit closed and conducting current, and reverse biased during the other half of the cycle, becoming open for that half cycle and stopping current flow. The end result is that the heating element is only getting about 60 vdc instead of 120 vac.

Not getting that forward and reverse bias thing? Don’t worry– we go into detail on that in the Fundamentals training course.

Some old-timers may be saying, “I been fixing appliances for 40 years and I never needed to know nothin’ about no Ohm’s Law. Sounds like more useless engineer stuff to me. I don’t need no stinkin’ Ohm’s Law!”

These are usually the same guys who can’t read schematics or use them to troubleshoot and are utterly lost on the new electronically-controlled appliances with multiple control boards. These guys are dinosaurs who will soon be extinct. Appliances circuits are only becoming more complicated, not less.

Gone are the days when you could just jumper out a handful of parts one by one until you found the bad part. You have to know how to troubleshoot electrical circuits and knowing Ohm’s Law is foundational to that. This applies to the new stuff as well as the old stuff. For example, without knowing how to use Ohm’s Law for circuit analysis, you’ll never figure out how this simple old-school electric dryer circuit works.

Understanding Ohm’s Law and circuits is one of the foundational skills for being a technician. In fact, if someone doesn’t know this stuff, they’re not really a technician— they’re just a parts changer. What’s the difference? Technicians understand how circuits and appliance systems work so they can use the schematic and specifications to do analytical troubleshooting and figure out the problem even on appliances they’ve never worked on before. Parts changers, on the other hand, rely on patterns they’ve previously encountered so their “troubleshooting” goes like this: “If this problem, replace that part.”

If you want to be a genuine appliance technician who can figure out how to fix anything, then start with the Fundamentals of Appliance Repair training course here at the Samurai Tech Academy.

Then take the Advanced Schematic Analysis and Troubleshooting training course to get advanced instruction on troubleshooting appliances with multiple electronic control boards.

This presentation on Ohm’s Law is one of the many enlightening technical presentations in the Basic Electricity module of the Fundamentals Course.

When there is a no-ice complaint, sometimes the icemaker is fine and instead the plumbing or installation is to blame. Low water pressure to a refrigerator can cause undersize icemaker cubes and result in the icemaker jamming during harvest. But how much water pressure do you need? And how do you determine what the pressure is? What does that look like?

The exact water pressure requirement for a particular make and model of refrigerator is specified in the installation manual, which no one reads. Nonetheless, it is there, so the manufacturers have made a good-faith effort to get that information out there. It’s not their fault that most people who install wet appliances (hello, plumbers) and most appliance techs, for that matter, refuse to read these specifications or gloss over them with a “Yeah, whatever.”

But there’s good stuff in there! Most refrigerators require a minimum of 20 to 40 psi. The exact minimum is spelled out in the installation instructions. Most GE refrigerators, for example, require a minimum of 40 psi water pressure for the ice maker to work properly. Samsung requires a minimum of 20 to 30 psi depending on the specific model. As a rule of thumb, all refrigerator ice makers will work properly with a minimum of 40 psi water supply pressure.

But how can you tell what the water pressure is? Well, you could use a pressure gauge to measure it but, UGH!, what a freakin’ hassle!

Wouldn’t it be awesome if you could calibrate your eyeballs to tell when water pressure was less than 20 psi just by looking at a discharge stream from the 1/4″ supply tube? Ya sure, ya betcha! And now you can do exactly that with the Samurai Calibrated Eyeball Water Supply Pressure Assessment Technique™ (SCEWSPAT, pronounced, “skew-spat”).

Using my patent-pending SCEWSPAT technique, you can determine the pressure of any refrigerator icemaker water supply line using only your soon-to-be calibrated eyeballs! In this video, you will see what an inadequate water supply pressure looks like.

In general, if you disconnect the water supply tubing from the refrigerator, open the valve and see a lame, pee-pee stream of water, you done found a major problem, Hoss! That obvious problem has to be fixed first before you can determine if the icemaker is operating properly or not.

As mentioned in the video, an adequate water pressure (20 to 40 psi) exiting the 1/4″ water supply tubing should be coming out with enough force to knock over a cup. At 20 psi, a 1/4″ tubing is exerting almost a pound of force on the cup’s sidewall. That’s a lot and will knock over any cup!

Need more specifics? Okay, try this…

The specifications for the dispenser stream in a GE refrigerator is 13.5 oz/20 seconds. This is close enough to all the other manufacturer’s specs that we can call this a universal spec.

Now, take a two-cup measuring cup (borrow from customer) run the dispenser and time it. If it doesn’t fill 13 oz (or 400 mL) in 20 seconds, Houston, we have a situation. After doing this just a few times you will have calibrated your eyeballs so that you don’t have to use the measuring cup/timer method again. Let’s hear it for SCEWSPAT!

Learn more about how to kick refrigerator and icemaker bootay in the Samurai Tech Academy’s Refrigerator Troubleshooting and Repair training course!