Sam Brown

[Sam Brown]

The answer is True. You will probably never be in a situation as a technician where you have to measure DC current. DC voltage you will absolutely measure many times. But not DC current. It’s simply not a diagnostically useful measurement.

[Sam Brown]

Great question! A couple of pointers I can give you to clear things up:

First, make sure you pay attention to the Samurai’s exact wording in that addendum video. He doesn’t say that the two ways of the drawing the circuit are perfectly equivalent. He just says that, as far as the power supply is concerned, the current draw is the same, and it changes in the same way if one of the loads were to go open.

You’re correct that point A and point B are not electrically equivalent. That’s because those lower three circuits are just an “exploded” version of the three parallel branches. To make A equivalent to B, you need to place A in the topmost parallel branch, at some point after the load. Where A is located currently is a point that doesn’t exist in the three exploded circuits.

If that still isn’t clear, let me know!

[Sam Brown]

Hey Kevin,

Thanks for your patience! After the discussion that Susan mentioned above, we’ve edited some of our wording in the course with reference to the Systems troubleshooting approach. You can see it for yourself in Module 2, Unit 1, but the 4 systems are called out like this:

1. The Refrigeration System: compressor, condenser, evaporator, refrigerant, associated tubing, and the condenser fan.
2. The Air Distribution System: evaporator fan, damper, door and door seal, and air return port.
3. The Temperature Control System: thermostat or, depending on the design, the thermistor and control board.
4. The Defrost System: defrost heater, defrost bimetal or thermal cutoff, evaporator thermistor (if used), and defrost drain system.

As you can see, the condenser fan is classified as part of what we call the Refrigeration System, which also includes the entire sealed system.

Now, getting back to the question that started this, we haven’t changed any of the wording on that, because it’s still correct. While the condenser fan is a part of the Refrigeration System, it is not part of the sealed system, since that refers exclusively to the compressor and all the sealed tubing that carries the refrigerant (both the condenser fan and the sealed system are part of the Refrigeration System, though).

Hope that clears things up! Let us know if you have any more questions.

[Sam Brown]

The condenser fan does play a key part in helping to cool off the refrigerant as it passes through the condenser coils, but it is not part of the sealed system itself. It’s part of the refrigerator’s air distribution system.

[Sam Brown]

Hey Kevin,

Think carefully about the wording of the question. “Two common sealed system problems encountered in the field are:”

So this isn’t a question about refrigerator problems generally, but specifically about sealed system problems. Your answer contained one item that’s a sealed system problem (weak compressor), but another that wasn’t (bad condenser fan motor). Look for the answer that contains only sealed system problems.

[Sam Brown]

Hey Kevin, thanks for posting your question in the forum!

The columns on that chart are grouped so that, for any particular temperature, the corresponding ohms and volts readings are to its right, not its left. With this in mind, take a look at the chart again and see if your findings correspond with the answer given.

[Sam Brown]

You’re correct that the main control sends a DC PWM signal to the inverter. But the inverter sends electronically commutated AC voltage to the BLDC compressor. The PWM signal tells the inverter what frequency and amplitude the voltage it sends out should be.

[Sam Brown]

Yes, that’s correct — you cannot look at the quiz answers again unless you start another attempt. But I’m happy to tell you want the possible answers for that question were! They are:

A. variable frequency
B. pulse width modulated
C. split phase

[Sam Brown]

Ha! Thanks for posting that — I was curious what you were talking about. That’s certainly the kind of thing you would have seen over at Appliantology. A little too extracurricular for the courses at this site. 😀

[Sam Brown]

As mentioned in the video, there’s a lot of terminology that manufacturers throw around when it comes to direct spark ignition systems, so don’t feel bad about getting a little turned around. Fortunately, it’s not as confusing as the terminology makes it out to be.

A direct spark ignition system is just any burner system that ignites gas with a spark. As simple as that. There are a lot of variations depending on whether there’s flame sensing or whether all the burners spark at the same time, but the fundamental principle of ignition is the same.

Now go back to that question that was confusing you with this in mind. How many of the listed systems use a spark to light the gas coming out of a burner? Some of them? None of them? All of them?

Let me know if it’s still not clear.

[Sam Brown]

Consider yourself familiarized with the forums!

As for that video, I’m not sure which one you’re referring to. Did you see it here at Master Samurai Tech, or was it over at Appliantology? If you can find it on YouTube, post the link to it here — I’ll see if it rings a bell.

[Sam Brown]

That’s an excellent observation and a great question!

The beef is this: there’s more that can impede the flow of current than just resistance. In fact, there’s a whole other category of impedance that’s called reactance.

While reactance isn’t present to a significant degree on all loads, a lightbulb is an example of a reactive load. So that explains why you’re getting lower amperage than you would expect.

We’ve got a great video on the topic of reactance that you should check out. It uses a motor as an example of a reactive load, but the principles in play are the same as what you’re seeing with your lightbulb. Here’s a link to the video: https://www.youtube.com/watch?v=n9gaaKtOfDQ&feature=youtu.be

[Sam Brown]

“Voltage drop” and “voltage difference” are actually two distinct terms for two distinct things. Here are a couple of examples.

You have a circuit supplied with 120 VAC. In this circuit, there is a switch that is currently open. If you put one meter probe on either side of the switch, you would read 120 VAC, because there is 120 volts on one side of the switch and 0 volts on the other side. There is clearly a voltage difference here, but no voltage drop, because there’s no current flowing through that open switch.

Now, imagine that you have another circuit, this one also supplied with 120 VAC. This circuit is closed, with current flowing through it. There’s a heating element in the circuit, and you place your meter probes on either side of the element. Like in the previous example, you read 120 VAC, but it’s not because the element is open — it’s because there’s a voltage drop of 120 volts across the element, and that’s what you’re reading with your meter probes.

It may seem like a subtle distinction, but it’s important to understand, because those are two very different situations electrically. For further clarity, I recommend that you click here to review the videos in the Voltage Drop and Load unit of the Fundamentals course.

[Sam Brown]

In the fundamentals course, we learned that if you check the voltage at the load on a 120 VAC circuit, you should get a 120 VAC voltage drop or a reading of 0 VAC on the meter.

You’re a little bit off on your understanding of voltage drop there. Let me see if I can clear things up.

Remember that when you measure voltage, what you’re actually doing is measuring the voltage difference between two points. Those two points are where you’ve placed your meter probes.

When a load has current flowing through it, there’s going to be voltage drop across it, as you said. But that means that you’re going to read 120 VAC when you put your leads on either side of the load, not 0 VAC. The difference between those two points (a difference created by the voltage drop across the load) is 120 volts, and so that’s what your meter shows.

Does that help explain it?

[Sam Brown]

Good question, John!

The diagram that you’re looking at in the Kleinert text is for one specific compressor design. The phrasing of the quiz question is meant to be more general, which is why we don’t mention a connecting rod.

Thanks for asking!

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