Sam Brown

[Sam Brown]

Great! Glad to hear it.

[Sam Brown]

Not at all — in this example, we’re just showing the board closing the internal connection between J1 pin 1 and J2 pin 8. The other pins on those connectors all have different functions. Some are for supplying neutral, some for line, and some (like the terminals for the thermistors) supply low voltage DC power. J1 pin 7, as an example, supplies line to the compressor whenever the board chooses to run it.

That’s the power of control boards — they may act as switches sometimes, but they’re very smart switches that can switch line and neutral to lots of different loads intelligently.

[Sam Brown]

Think about what’s present at each of those points your leads are on. At J1 pin 6, you have line voltage — 120 VAC.

And then at J2 pin 8, you have neutral. That may not be as easy to see, but that’s why the Samurai drew in that blue closed switch on the control board. The board is acting simply as a closed switch, making J1 pin 1 and J2 pin 8 electrically equivalent points.

So when you put one lead on line and the other lead on neutral, what will your meter measure?

[Sam Brown]

In a split-phase compressor, the start and run winding are arranged in a “V” shape. The point of the V is where the Common terminal is, and the two lines that extend from that point are the windings. The Start and Run terminals aren’t directly connected to each other, since they’re each at the end of one of the lines of the V.

This is why you always measure the most resistance when you put a lead on the Start terminal and one on the Run terminal. When you do that, you’re reading the resistance of both the start and the run windings.

Does that make sense?

[Sam Brown]

You’re heading in the right direction!

When a circuit uses 120 VAC, that means it’s using just one leg of the household power supply — either L1 or L2 (doesn’t matter which).

The reason why we call split-phase motors “split phase” is because of the two windings they have — run and start. Due to the way these windings are configured relative to each other, the magnetic fields produced by the current flowing through them is out of phase. They’re not 180 degrees out of phase like L1 and L2. Depending on the motor, they can be as little as 30 degrees out of phase. But that little difference in phase is enough to get the motor going from a dead stop.

So split-phase motors take single phase power, but the start winding creates a second phase for as long as it’s in the circuit.

Let me know if anything still isn’t clear.

[Sam Brown]

The purpose of a grounding wire is to keep the neutral side of the power supply at ground potential — i.e., 0 volts. Ground should not be high resistance. The entire point of it is to be a 0 resistance path to ground. If a grounding wire becomes high resistance, that is actually a fault condition.

Because the grounding wire keeps neutral at ground potential, you can safely touch a neutral wire without any risk of electrocution, even if there’s hundreds of amps of current flowing through it. If the path to ground were to become high resistance, however, then there could become a voltage difference between neutral and ground, which would cause you to get shocked when you touch neutral.

I think this video will help to explain these concepts further.

[Sam Brown]

I have had a number of instances(especially in microwaves running on an AFCI) where there is repeated tripping of the AFCI breaker.Have had licensed electricians out who have said that microwaves create an arc fault condition.

We actually cover this in module 2, unit 6 — AFCIs work by comparing the electric wave pattern to a database of acceptable patterns. This can mean huge databases covering thousands of different brands and types of appliances. And sometimes, there’s a particular model that produces a wave pattern during normal operation which isn’t in that category. That’s probably what you’re running into here.

As for why the surge suppressor helps, that’s because it’s helping to even out any spikes that would otherwise be present, making for a smoother wave pattern. There’s certainly no problem with fixing this issue by installing a surge suppressor. In fact, these appliances should be on surge suppressors anyway, so it’s strictly a good thing.

[Sam Brown]

All the Samurai is doing is looking at the measured pressure and temperature at each point and then marking the spot on the P-H diagram that corresponds to it.

For example, look at point #1 in the R134a system shown in the video — the one right at the compressor suction. You have 16 PSIG and 47 F there. Now you take that pressure and temperature, find the spot on the diagram where they intersect, and mark it.

Here’s the P-H diagram that was used in the video. A couple things to note:

The temperature lines change drastically depending on whether you’re looking within the saturation dome or not. If they’re in the saturation dome, they’re horizontal. If they’re outside it, they’re almost vertical. That’s representing how pressure and temperature are directly related within the saturation dome, but not outside of it.

Also, pressure on this chart is shown as PSIA (PSI Absolute) rather than PSIG (PSI Gauge) which is the value we’re given. I believe the difference between these was explained in the video. To convert from PSIG to PSIA, just add 14.7 to your PSIG value. That will give you the equivalent value in PSIA.

See if you can find the spot that corresponds to 16 PSIG and 47 F (without referencing where it is in the video, of course).

[Sam Brown]

Great questions! Let me lay it out for you best as I can.

1. Practical Sealed System Thermodynamics, Part 1. 19:26 into the webinar
At test point 1, 84psig: at the suction of the compressor:
Shouldn’t the superheat value be 21 deg F instead of 41 d deg F as in Webinar?

Yep, using the data that the Danfoss app has now, 21 F is the correct amount of superheat there. That webinar was recorded a couple years ago, and there have been a lot of changes to the Danfoss app since then, including data table corrections. Usually these corrections are only in the range of a few degrees or a few psi, but this is a big one — a 20 degree difference. I can only imagine that there was an error in the app’s data back then that has since been corrected. Good spot!

2. When I was using Dan Foss App to do the homework, I noticed there was selection to make between “Bubble” vs. “Dew”. After doing some searching on the internet, when doing the subcooling calculation should use Bubble, and for superheat should use Dew. Can you tell me why this is so. I know what the Bubble and Dew stands for by definition. I just want to know reason for: subcooling = use Bubble and superheat = use Dew in Dan Foss App. I also know for newer hybrid refrigerant like 404A there is glide between the bubble and dew point.

The bubble and dew points are just terms for referring to either side of the saturation dome on the P-T chart. The bubble point is on the left side of the dome, referring to when the liquid refrigerant is “just starting to bubble”. Conversely, the dew point is on the right side, referring to when the refrigerant is now almost entirely vapor, with “just a few drops of dew left”.

Since subcooling takes place to the left of the dome, you should use Bubble to calculate it. And since superheat happens to the right of the dome, you should use Dew to calculate it.

The reason why that Bubble/Dew switch exists (another feature that wasn’t around back when we recorded that webinar) is because R404a is a zeotropic refrigerant. That means that it’s made of a mixture of different substances that boil at different temperatures (unlike homogenous refrigerants like R134a). And as you pointed out, there is glide in zeotropic refrigerants like R404a. Glide means that the lines within the saturation dome are not parallel with the x-axis as they are in homogenous refrigerants.

For demonstration purposes, here’s a P-T chart for R134a, showing perfectly straight lines within the saturation dome. There’s no glide in this chart, which is why the Danfoss app doesn’t allow you to use the Bubble/Dew switch for R134a.

Now compare that to this chart of R407c, which has very pronounced glide:

And lastly, let’s get back to R404a, which is what you’ve been working with. The glide is much less pronounced here than for R407c, but it’s still there if you look closely.

Since R404a doesn’t have very significant glide, you’ll notice that values don’t change much depending on whether you have Dew or Bubble selected in the app. But because it’s a zeotrope, the bubble and dew points are different, and so you should select the correct one depending on if you’re calculating subcooling or superheat for the most accurate results.

[Sam Brown]

Great catch, Steve! There was actually an error in that question. It was supposed to clarify that it was specifically asking about timed dry. The centrifugal switch only completes the timer’s neutral in auto dry.

Thanks so much for catching that typo! The question has been clarified now.

[Sam Brown]

There are a few things that could cause inconsistent readings like that.

One would be if you have not isolated the component you’re measuring from the circuit. This is done by disconnecting one side of the circuit. This prevents backfeeding, which can compromise your measurement.

Another possible cause is simply poor contact with the measurement points. Unless your leads are dead on, you’ll get varying readings on your meter.

And yet another cause would be if you were measuring a component or circuit with reactive qualities, such as if there’s a capacitor in the circuit. Since your meter is actually sending a small amount of current through the circuit when it measures resistance, reactive components can mess with the reading.

Your takeaway should be this: ohms measurements are sometimes useful, but they are one of the least reliable measurements that your meter can do. The only time you should draw a diagnostic conclusion from ohms is if you measure that the component is completely open when it should not be. Any result other than that simply tells you that you need to proceed by using a more reliable and informative measurement, such as volts or amps.

[Sam Brown]

I wanted to get a better understanding why when testing pin 8 to pin 6 that’s line why it’s 120 volts even if there was a drop across the load.?

I didn’t see where in the video he did that measurement — could you give me the timestamp?

I think the best way for you to get a better grasp of why he did those measurements and what they meant would be to watch the original video he was referencing. Give it a watch and see if it makes sense — write me back if you’re still confused about anything!

https://www.youtube.com/embed/e_dG91lddS8

[Sam Brown]

It does sound counterintuitive, but it has to do with how those inlet valves are designed.

When these inlet valves close, they actually take advantage of the water pressure to keep their sealing plungers closed. There is a small spring that pushes the plunger down, but it’s not strong enough to make a tight seal by itself. The engineers designed it so that with the valve closed, water can fill the space above the plunger and exert pressure on it. At least 20 PSI of water pressure is required to make a reliable seal.

[Sam Brown]

Again, the pump does not run at all during agitation.

A small clarification on this, actually. In models where you have a pump that is physically attached to and run by the drive motor, the pump is technically spinning during agitation. But since it’s not spinning in the correct direction to pump water, it’s not actually accomplishing any work. It’s neither draining water from the tub, nor is it moving the water around in the tub. But technically it is moving, because it’s physically attached to the drive motor.

[Sam Brown]

But you don’t mention that there even is a water pump that is doing anything during the agitation section.

Correct — because the pump doesn’t run during agitation. Water and clothes get circulated during agitation by the rotation of the agitator, which is turned by the drive motor. The drain pump only runs when the washer needs to drain water from the tub.

When we say, “On some models, the main drive motor drives the pump by spinning in the opposite direction than it did during the agitation cycle,” we’re saying that the drive motor spins in the opposite direction than it did during agitation, and that’s how the motor drives the pump. Again, the pump does not run at all during agitation.

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